Đặc điểm cấu trúc kiến tạo phần tây bắc bồn trũng nông sơn, quảng nam và sự tạo khoáng urani trong cát kết tt tiếng anh

MINISTRY OF EDUCATION AND TRAINING HANOI UNIVERSITY OF MINING AND GEOLOGY Nguyen Truong Giang TECTONOSTRUCTURAL FEATURE AND URANIUM MINERALIZATION IN SANDSTONE OF THE NORTHWESTERN PART OF THE NONG SON BASIN, QUANG NAM PROVINCE Major: Geology Code: 9440201 SUMMARY OF PhD THESIS IN GEOLOGY Ha Noi - 2019 The thesis is completed at: The Department of Geology, Ha Noi University of Mining and Geology Supervisors:: Prof Tran Thanh Hai, PhD Assoc Prof Nguyen Phuong, PhD Reviewer 1: Prof.DSc Dang Van Bat Reviewer 2: PhD Nguyen Van Nguyen Reviewer 3: PhD Vu Quang Lan The Thesis has been evaluated by the Assessment Council for Doctoral Thesis under the University Level at……., … … 2019 at the Ha Noi University of Mining and Geology The thesis can be found at: - The National Library of Vietnam - Ha Noi University of Mining and Geology INTRODUCTION The necessity of research Vietnam is a country with high uranium potential, in which the sandstone - hosted uranium mineralization type in the Nong Son Basin is supposed to have the greatest potential and appropriate conditions for mining The sandstone-hosted uranium deposits and mineralizations are considered as important material input for development of the atomic energy sector The geological mapping and mineral survey at 1:200 000 and 1:50 000 scales have been implemented for The Nong Son Basin in general, the northwest area of the basin in particular; some of uranium potential areas have been investigated and evaluated at 1:10 000, 1:5 000 and 1:2 000 scales In addition, many scientific research projects on uranium minerals have been carried out by different geoscientists since 1975 to present days The above mentioned studies have addressed the problems at the various levels in terms of geology, tectonics uranium mineralization controlling contexts and the potential of uranium resources in the prospect areas The obtained results are important fundamentals to orient subsequent researches However, most of the research works only focussed on general distribution pattern of the uranium ores, lithological characteristics, ore composition, mineral content, and geochemistry, etc To date, no detail study on tectonics- structure and its linkage to the uranium mineralization has been implemented The interpretation on tectonics-structure, establishing deformation phases and reconsruction of geological history of the Nong Son Basin in general, and in the northwestern portion of this basin area in particular as well as the linkage to the uranium mineralization in accordance with principles of the Plate tectonics theory are necessary tasks in order to meet the practical demands These are important in delineation of the distribution pattern of the mineralization zone, the level of concentration, morphology of ore bodies in each area With such outcomes, the zoning of prospect areas and planing for surveying, evaluation and exploration on uranium within the investigated areas will be carried out effectively thereby In order to resolve the above-mentioned demands a thesis entitled: “Tectonostructural feature and uranium mineralization in sandstone in the northwestern part of Nong Son Basin, Quang Nam Province " was proposed for this study 2 Objectives of the research To define characteristics of tectonic - structural setting in the Northwest of the Nong Son Basin as well as its controls on uranium mineralization in sandstone in order to provide database for the orientation of subsequent investigation, evaluation and exploration programs Object and locality of the research - Object: Geological units, geological structure and uranium mineralization in sandstone - Locality: Northwestern area of the Nong Son Basin, Quang Nam Province and surrounding regions Major tasks of the research - Defining composition, pattern and age of major geological units as well as characteristics of uranium mineralization in northwestern portion of Nong Son Basin - Studying tectonics - structures of the northwestern portion of Nong Son Basin and and interpreting the constraint of the tectonic structures on uranium mineralization in sandstone of the study area - Establishing scientific and practical basis to orient surveying, evaluation and exploration programs for uranium in the northwestern portion Nong Son Basin Scientific and practical implication of the project 5.1 Scientific implication - The new data on geological structure, age and forming conditions of geological units and uranium mineralization presented in the thesis are impotant contributions to geological database of Vietnam - The reconstruction of geological history of the Nong Son Basin and the role of tectonic deformation for uranium mineralization are new findings that useful for the interpretiation of origin, distribution model, morphology of uranuium ore bodies in the study area in particular and the Nong Son Basin in general 5.2 Practical implication - The establishment deformation phases, reconstruction of geological evolution of the northwestern part Nong Son Basin in particular and the Nong Son Basin in general as well as their controls on uranium mineralization in sandstone provided practical contributions in planing of surveying, evaluation and exploration works in the Nong Son Basin - The establishment of premises, indicators and delineation of potential areas for uranium mineralization in sandstone within the study area are considered important scientific basis in proposing subsequent surveying, evaluation and exploration activities in potential areas of the northwestern part of Nong Son Basin Theoretical point of view - View point 1: The northwestern part of Nong Son Basin has experienced complex tectonic deformations, in which the Middle Triassic Jurassic sedimentary rocks unconformably overlying the deformed preMesozoic basement rocks have been strongly affected by deformation phases The post-deposition tectonostructural elements are important controls on uranium mineralization in sandstone of the study area - View point 2: The uranium mineralization in the study area has been formed in different periods, which spanned from ~144 to 14 Ma The uranium mineralization has initially been produced by the redox mechanism and accummulated along the redox front formed by the interection of oxidating fluid and reduction elements within the coarsegrained clastic sedimentary rocks of the An Diem Formation The continuous impacts of subsequent deformational events have led to reworking of previously formed mineralization and deposting secondary mineralizations at various ages New findings of the thesis - The study results have identified the nature of various structures, establish and classify deformation phases, reconstruct tectonic evolution of the northwest part Nong Son Basin as well as to interpret linkage of uranium mineralization to the tectonics - structure of the study area The northwest part of Nong Son Basin has been strongly affected by deformation phases, in which the 1st phase affected the pre-Mesozoic basement rocks while other deformation phases have modified all rocks, including the Mesozoic sedimentary formations - The new results have contributed to the identification of the linkage between the rock deformation and uranium mineralization, suggesting that post-deposition deformations have controlled uranium mineralization in the Northwest Nong Son Basin - The uranium mineralization occurs in coarse-grained clastic sedimentary rocks, which have been deposited and reworked in periods spanning from ca 144 to 14 Ma Uranium has been accumulated in the rock as the result of post-deposition redox processes, in which ore was deposited along along the redox front as the the mixing of oxidation fluid and reduction elements Mineralized zones were produced, remobilized, altered and redeposited in a complex pattern due to continual impacts of the multiphase regional deformation - The results have provided premises and indicators for surveying and delineating potential areas of uranium mineralization at various levels within the northwestern portion of Nong Son Basin These are important scientific basis for surveying, evaluation and exploration of the uranium ore in the study area Structure of the thesis In addition to the preface and conclusion part, this thesis contains four chapters: Chapter Overview of the northwestern part of Nong Son Basin Chapter Basic principles and research methodology Chapter Geological setting and uranium mineralization of the northwestern part of Nong Son Basin Chapter Tectonostructural feature and its role for uranium mineralization in the northwestern part of Nong Son Basin Database for the thesis The thesis was completed based on documents directly collected, processed and interpreted by the candidate during carrying outscience researches and geological surveying at the Geological Division for Radioative and Rare Elements Especially, field data and sample analytical results gathered since 2010, including: - Gelological mapping and mineral survey reports at different scales available for the study area, especially field investigation data on geological structure and sampling analysis clollected and processed by the candidate - Updated data on field investigation, geological mapping, tectonicsstructure studies in the northwestern part of Nong Son Basin completed by candidate during this thesis preparation - New data on thousands of samples analysed for uranium chemical contents, hundreds of thin section and ICP-MS, and organic carbon analyses, suppoted by the Uranium exploration project in Pa Rong- Pa Lua area that is hosted by to Geological Division for Radioative and Rare Elements Especially the analytical results of convential U-Pb dating samples to determine absolute age of magmatic rocks; samples to determine provenance age of the sedimentary rocks used SHRIMP and LA-ICP-MS methods; sample analysed absolute age of uranium ore have been ontained by the candidate during the thesis preparation - The published materials consisting of thematic material, scientific reports, articles related to study area; the documents obtained from prospecting, geological baseline surveying works, evaluation and exploration programs carried out by Geological Division for Radioative and Rare Elements within and surrounding the study area In addition, the candidate also collected other scientific research papers, books, journals on uranium mineralization from domestics and foreign providers 10 Traininng Institution The thesis was completed at the Department of Geology, Faculty of Geoscience and Geoengineering, Hanoi University of Mining and Geology 11 Acknowledgment The candidate would like to gratefully thank to Prof Dr Tran Thanh Hai and Assoc Prof Dr Nguyen Phuong, who have enlightened and supervied the candidate throughout researching process as well as their unconditional support completing this thesis I would like to acknowledge the Department of Geology, Faculty of Geoscience and Geoengineering, Department of Postgraduate Training, Directory Board of Hanoi University of Mining and Geology in providing generous support for the candidate to complete the thesis I also would like to send my sincere thanks to the scientists of the Department of Geology and Mineral of Vietnam, Geological Assocciation of Vietnam, Institute of Geosciences and Mineral Resources of Vietnam, Geological Institute of the Academy of Science and Technology of Vietnam, Russian Geological Institute(VSEGEI), the Institute of Geosciences and Mineral Resources of Korea (KIGAM), Rare Trace Elements Laboratory (Laboratory of Critical Elements) of the University of Science and Technology AGH of Poland, Radioactive and Isotope Laboratory of the Institute of Geology-Geophysics of the Chinese Academy of Sciences., and all colleagues in Geological Division for Radioative and Rare Elements, for they generous supporting in analyzing of the high-quality samples as well as created favorable working environment for the completion of this thesis Chapter OVERVIEW OF THE NORTHWESTERN PART OF NONG SON BASIN Location and geological setting of the research area The northwestern part of Nong Son Basin is situated in the Dai Loc, Nam Giang and Tay Giang districts, Quang Nam Province, which extends over ~1000 km2 1.1.1 Tectonic position of the study area Tran Van Tri and Vu Khuc et al (2009) proposed that the study area belonging to an intracontinental rift system, which occurred after the Mesozoic Song Bung - An Khe collision and overlies the Early - Middle Paleozoic Quang Da Orogenic Belt and the pre-Cambrian Kon Tum Massif; it is a complex structure, which was formed during the Paleozoic orogeny and was subsequently deformed in Mesozoic Tran Thanh Hai et al (2014) reckoned the northwestern part of Nong Son Basin has been resulted from an extensional process following a post-Indochina-Sibumasu collision event 1.1.2 Geological setting of the study area 1.1.2.1 Geology of the Nong Son Basin a Metasedimentary and sedimentary units Pre-Cambrian units: Consist of sedimentary and vo,lcanic rocks, which have been metamorphosed to amphibolitic facies of the Kham Duc - Nui Vu complex (NP3-Є1kv) Early Paleozoic sedimentary units: Comprise mainly terrigenous sedimentary, carbonatic-terrigenous, carbonate and shaly sequences, which are intercalated by intermediate - acid volcanic rocks and theirtuffs, which are grouped to of the A Vuong Formation (Є2-O1 av) The rocks have been metamorphosed to green-schist facies Mesozoic sedimentary and volcanic units: extensively filled and exposed in the Nong Son Basin which includea number of formation such as Song Bung (T2sb), An Diem (T3nađ), Suon Giua (T3n-r sg), Ban Co (J1bc), Khe Ren (J1-2kr) and Huu Chanh (J2hc) Cenozoic sedimentary and volcanic units: Include Neogene sedimentary rocks overlain by the Quaternary unconsolidated sediments (Q) b Intrusive rocks Early-middle Paleozoic intrusive rocks: most are granitic rocks that extensively observed in the northern margin of the study area They are exposed as batholiths and/or minor dykes, which comprise part of the Dai Loc Complex (γaD1đl) Late Paleozoic - Mesozoicintrusive rocks: this formation was observed along the southern margin of the Nong Son Basin, it is characterized by diverse composition, mostly vary from intermediate to acidic rocks The rocks were sub-divided into the Ben Giang - Que Son (γδP2-3 bq), Chaval (aT3 cv), Hai Van (γaT3hv) and the Ba Na (γK-Ebn) Complexes 1.1.2.2 General tectonic deformation of the Nong Son Basin The strong and superposed tectonic deformations have led to significant change in the order, attitude, continuity and geological relationship of the rocks The pre-Mesozoic units have been entirely disturbed The subsequent superposing tectonic activities have transformed and modified the older structures, creating complicated regional structural interference pattern s Development of the geological formations and deformational events in Nong Son Basin all have been associated with evolution of the continental crust due to the continuous convergence and collision of tectonic plates into the margin of the Indochina Block in the Phanerozoic Previous studies on geology and uranium mineralization of the study area 1.2.1 Before 1975 Mainly are regional geological mapping and mineral discoveries achieved by both French and Vietnamese geologists 1.2.2 After 1975 The regional geological survey and uranium studies were only conducted after 1975, mostly after 1980 once several uranium occurrences were discovered in the Nong Son Coal Mine, especially uranium mineralizations in sandstone of the Nong Son Basin was discovered Many projects on geological survey and uranium potential evaluation have been conducted Regarding researches on uranium mineralization, there have been several scientific studies on origin of the uranium ore formation, depositional environment as well as the source of uranium ore in Nong Son Basin (Trinh Xuan Ben, 1995), or classification and relating of uranium mineralization types to the classic deposit model in the world (Nguyen Quang Hung, 2002) Exisiting problems in the previous studies The previous studies on uranium have only focused on uranium potential in saperate areasand porposed orientation for porspecting and exploration works The researches on geological setting, tectonicstructure, uranium mineralization, petrology, facies geochemistry, depositional environment, etc In the Nong Son Basin have only been carryied out at larger scale of a regional geological context, lack of detail data and quantitative studies Characteristics of deformation, evolutionary history of the Northwestern Nong Son Basin and their linkage to the uranium mineralization in sandstone have been addressed in some scientific documment, but they demonstrated limitedr data The study on uranium mineralization in sandstone just has only been implemented in terms of depositional mechanisms while other controlling elements such as age of uranium ore formation, tectonic regimeduring the sedimentary deposition, uranium mineralization, accumulation rule and uranium distribution pattern in each period of sedimentation have not been well defined The above mentioned existence need to be well defined The study on tectono-structure and reconstruction of evolutionary history of the northwestern part of Nong Son Basin will contribute to interpretation of ore forming mechanism, distribution of the uranium ore bodies in the study area This is one of the proper approaches in solving the problem of origin, ore forming conditions and distribution rule of the uranium ore in the study area Chapter BASIC PRINCIPLES AND RESEARCH METHODOLOGY 2.1 Basic principles of uranium mineralization in sandstone 2.1.1 Uranium deposit models in sandstone 2.1.1.1 Overview of uranium deposits in sandstone Uranium deposits in sandstone are uranium accumulation, which are largely resulted from oxidation-reduction (redox) process occurring in sandstone units of the molasse lacustrine and fluvial formations The uranium deposits in sandstone are often formed at the margin of the basin and are accumulated in the coarse grained rocks such as sandstone, coal- 15 Que Son and Hai Van complexes Geochemical and isotopic properties of this stage show the I-type graniteformed in island arc or active continental margin seting - Stages 3: Consisting of peralluminous, S-type alaskitic granite, which was formed at 252 ÷ 241 Ma This formation includes the rocks have been partly defined as the Ben Giang - Que Son Complex and part of the Ba Na Complex Geochemistry and isotopic signature of these rocks reveal that they are syn-orogenic granite 3.3.2 Age of provenance of the uranium-bearing sedimentary rocks Detrital zircon grains separated from a coarse-grained, uranium hosted sandstone samples (GK 26604/1) in Pa Lua - Pa Rong area were dated by SHRIMP technique at the Institute of Geology and Mineral, Korea (KIGAM) The results showed that the age of detrital zircons varies from the oldest age of ca 2642 Ma to the youngest age of ca 252 Ma., while most of the grains (8/19 grains) centre around 492 ÷ 463 Ma Five grains concentrate on interval of 1330÷1728 Ma while two grains are ca 2083 ÷ 2642 Ma., one grain is at 590 Ma and another grain is at 252 Ma One grain was dated at both margin and core of the grain The age between different point are also different: 1330 Ma for margin and 2083 Ma for core,demonstrated that this zircon grain has been strong recrystallized at 1330 Ma The ca 252 Ma zircon grain retained its euhedral shape, indicating that it had not been transported siginificantly from its magmatic source, meaning that the grain has been generated from a proximal source region In order to further verify the age and provenance evolution of the sedimentary sources of the uranium ore-bearing sedimentary rocks in the study area, another sample of uranium ore-bearing coarse-grained sandstone (GK 26604/2) located at 85.4÷90.4m depth of GK 26604 Drill hole in Pa Lua - Pa Rong area was collected for dating by LA-ICP-MS technique at the Pheasant Memorial Laboratory, Okayama University of Japan The U-Pb age distribution spectrum shows that most of the zircon grains were crystallized during the age interval of 252÷336 Ma (corresponding to the Permian- early Triassic Period) and of 468÷483 Ma (corresponding to Ordovician period) There were two grains showed the age at 231 (+/-6) Ma., two grains aged at 227 (+/-6) Ma., one grain showed the age at 221 (+/-5) Ma The common crystallized ages occcurred in Ordovician and Permian- early Triassic period indicate that that most of zircon grains and assocciated sedimentary materials have been generatedfrom magmatic and metamorphic rocks surrounding the area, 16 which have been rapidly exhumed during the orogenies of the Indochina Block The above analysed results, suggest that the source of sediments in the study area have likely been eroded from the various geological units as follows: a 1st Age interval: comprises zircon grains older than ca 700 Ma mainly from recrystallized and highly metamorphosed zircon grains The source for these zircons has not been well defined because the oldest metamorphic rocks surrounding the Nong Son Basin are high metamorphosed sedimentary rocks of the Kham Duc - Nui Vu Complex have the youngest age of ca 700 Ma (Tran et al., 2014) b 2nd Age interval: Spanning from ca 600 ÷ to ca 490 Ma appeared in some zircon grains are not correspond with any intrusive bodies nearby the study area c 3rd Age interval: Spanning from ca 480 to ca 380 Ma is most common age interval identified in all samples analyzed by both SHRIMP and LA-ICP-MS methods This age spectrum is coincided with the island arc and orogenic magmatic rocks surrounding the Nong Son Basin d 4th Age Interval: Varying from ca 300 to ca 221 Ma is the most common age interval in samples dated by LA-ICP-MS method The presence of ca 221 Ma detrital zircon grains in sediments imply that the age of the youngest deposition must be at least at ca 221 Ma This means that the oldest age for uranium-hosted sedimentary rocks in the study area should be at 221 Ma., corresponding to the Norian Stage (227 ÷ 208 Ma.) Thus, the An Diem Formation should be of Norian This age span is also similar to the third stage of intrusive magma as described above It is suggested that parts of the sedimentary materials for the An Diem Formation have been generated from the Early Triassic magmatic rocks that formed the base and exposed surrounding the area 3.3.3 The age of uranium ore The first time in Vietnam an absolute age of the uranium ore has been dated In order to date the uranium, uranium ore samples within an ore body located at the depth 80.4 - 81.4m of drill hole No GK 26604 in Pa Lua - Pa Rong prospect area with an U3O8 content up to 5.68% have been collected for dating Samples were preparated and dated at Laboratory for Low Grade Elements of Faculty of Geology, Geophysic, Environmental Protection, AGH University of Science and Technology (Krakow, Poland) Result of age dating for coffinite mineral showed that age span of uranium minrealvaries greatly, demonstrating a complex history of the 17 uranium mineralization in the study area According to this result, four stages of uranium mineralization were defined as follows: The oldest stage formed at 144 Ma., the next stage spans from 122÷73 Ma.; the third stage of 51 ÷ 23 Ma while the youngest stage was formed from 17 to 14 Ma In which, the first three stages were related to tectonic activities and basin formation where as the youngest stage can be resulted from exogenous process Therefore, it can be seen that history of the ore forming and alteration in the study area are closely related to different techtonic events that have been occurred for a long period of regional geological development The oldest mineralization stage took place at 144 Ma., corresponding to the early Cretaceous, once the Jurassic products were deposited, and the study area was uplifted to the continental environment, much younger than the age of the host sedimentary rocks contained uraimun ore that were deposited at 221 Ma (coressponding to Carnian period) The difference in the age of the mineralization in the study area also suggests that the mineralization in this area have entirely been resulted from secondary processes comparing to the age of the host rocks It means that the primary sedimentary processes have not produced ore bodies, or in other words no syn-deposition tabular ore bodies have been formed in the study area Chapter TECTONOSTRUCTURAL FEATURE AND ITS ROLE FOR URANIUM MINERALIZATION IN THE NORTHWESTERN PART OF NONG SON BASIN 4.1 Overview As stated above, tectonic deformation in the Northern margin of the Kon Tum Massif in general and northwestern Nong Son Basin in particulary has experienced a long and complex history, through multiphase superposed deformations and resulted in formation complicated tructural plan-view Each tectonic activity was normally associated with a regional event 4.1.1 Tectono-lithological assemblage a Neoproterozoic - early Cambrian active continental margin tectono- stratigraphic assemblage: This assemblage includes sedimentary and volcanicrocks, intrusive complex, which have been formed from ~Neoproterozoic to early Cambrian In which, the Kham Duc – Nui Vu Complexare exposed as a tectonic wedge along shouthren egde in 18 southeastern study area These complex has been strongly deformed, highly metamophosed at amphibolite facies, forming foliation, banded andstrip structures Garnet, silimanite or kyanite were discovered in some places contained, typical for amphibolite facies formed at medium pressure (Usuki and others, 2009; Tran and others, 2014) b Late Cambrian - Ordovician active continental margin tectonostratigraphic assemblage: Includes the rocks of the A Vuong Formation (€2-O1av) occurred in the northwestern and the northern margins of the Nong Son Basin Its major composition are fine grained clastic sedimentary rocks, intercalated by carbonatic layers This formation has been strongly deformed and highly metamophosed at greenschist facies, demonstrating a strong regional deformation process c Silurian - Devonian syn-orogeny assemblage: Consists of strongly deformed batholiths of the Dai Loc Complex (γ33 aD1đl), whose age spans from 430 ÷ 416 Ma Geochemical characteristics of the complex showed that they are syn-orogeny magmatic blocks produced by deep burial and melting of sedimentary rocks during the Ordovician - Silurian orogeny (Tran et al., 2014) d Middle Carboniferous – Permian active continental margin assemblage: Composed of I-type intrusive magmatic rocks with diverse composition, including gabrodiorite, diorite, granodiorite and granite, which were previously defined as the Ben Giang - Que Son and Hai Van complexes Isotopic and geochemical signatures show that they belong to the island arc or active continental margin magmatism e Triassic pre- to syn-orogeny intracontinental rift assemblage: characterized by sedimentary and intrusive magmatic formations, which are widely observed in the study area + Intrusive assemblage is composed of peraluminous, S-type magmatic rocks formed in the 3rd stage during ca 252 ÷ 241 Ma Previously, a part of complex has been classified into the Ben Giang - Que Son Complex and other parts ware of the Chaval, Hai Van, Ba Na complexes + Volcanic- sedimentary assemblage of the Song Bung Formation (T2 sb) + Terrigenous assemblage of the An Diem Formation (T3a ađ) + Grey molasse rocks including coal-bearing sedimentary rocks of the Suon Giua Formation (T3n-r sg) In comparison to the current existing data, the research results suggest that the Triassic intrusive, volcanic and sedimentary formations are closely related to the orogenic activities trigged by collision between the 19 Cimmerian (Sibumasu) – Sukhothai - Indochina blocks in Triassic period, resulting in formation of the Indosinia orogenic event (Metcalfe, 2013) f Early-Middle Jurassic syn-collision assemblage: includes Early Middle Jurassic coarse grained, continental red-bed sedimentary rocks of the Ban Co (J1bc), Khe Ren (J1-2 kr), Huu Chanh (J2hc) formations They fluvial sedimentary rocks deposited in continental environment during the Jurassic by post-orogenic movement and basin destruction g Unconsolidated Quaternary formation: Locally covers a limited area in the northeast of the study area 4.3 Deformational characteristics Based on the integrated data interpretation, the deformational structures in the area can be subdivided into generations that have been formed in at least different deformation phases  1st deformation phase (B1): The first deformation phase (B1) has formed before sedimentary formation in Nong Son Basin have been deposited and is characterized by entirely ductile deformation occurred in the intrusive and sedimentary rocks surrounding the Nong Son Basin In the Southern margin of the basin, deformation phase B1 is characterized by a high deformation zone containing compressed, stretched, folded and fractured tectonic mélange of the ultramafic, mafic, felsic or sedimentary rocks These blocks are surrounded by mylonite and ultramylonite, which are considered as a part of the Tam Ky - Phuoc Son Suture Zone  2nd deformation phase (B2): Typical structures for this phase are tight and inclined folds associated with large-scale thrusting shear zone developed in the Late Triassic - Early Jurassic rocks Under the impact of the northeast-southwest verging tectonic activities, the second anticline, syncline and overturned folding generation, whose axis oriented in northwest-southeast direction have been formed There folds commonly demonstrate narrow hinge zone, dip angle in two flanks varies from 30o to 75o, steeply deeping axial plane Associating with development of the 2nd folds are development of ductile, ductile-brittle thrusting shear zones, which are are sub-parallel to the axial plane of the folds The existence of these zones observed in sedimentary rocks of the An Diem, Suon Giua and Tho Lam formations, together with the presence of the folds demonstrated that these structure were related to a regional tectonic compression regime happened at the end of the Early Jurassic, resulting in formation of foldthrust structure and deformation of sedimentary rocks in the Nong Son Basin 20  3rd deformation phase (B3): Is characterized by northeast-southwest trending opened folds and northeast-southwest trending sub-parallel brittle to ductile-brittle faults, forming major structural grain of the Nong Son Basin and modified structural pattern formed during 1st and 2nd deformation phases The presence of the 3rd folding generation were observed in the southwest and central parts of the study area At the end of 3rd deformation phase, a number of strike-slip, diagonal-slip or reverse faults have developed forming large-scale zones sub-parallel to the axial planes of the 3rd folds across the study area These faults resulted in the formation of a tectonic wedge in the south and north of the study area  4th deformation phase (B4): took place in plastic-brittle mode and is characterized by 4th folding generation, whose axial planes are vertical to inclined developing in sub-meridian direction.The folds in the 4th deformation phase are commonly, gentle, kink-style, minor and in small scale, which were observed in some places  5th deformation phase (B5): characterized by brittle deformation, including broken zones, strike-slip, normal and reverse faulting systems oriented in sub-meridian and northwest- southeast directions These structures were evidenced by faulting scarps, brecciation, fault gauge This faulting systems crossed and displaced the pre-existing structures of 1st to 4th phases, shifted modern drainage systems and intensified weathering of original or young sedimentary formation It is suggested that they are the youngest structures in the region 4.4 Deformation-associated metamorphism The 2rd deformation phase is characterized by superposed metamorphism occurred during the Late Permian - early Triassic This phase has led to formation of the widely developed ductile shear zones together with infiltration of hydrothermal quartz veins and quartzitization of coarse grained clastic terrigenous sedimentary rocks at the base of the basin consequently, the rocks have been compacted, their porosity has been and hence migration of groundwater through the rock has been limited This change has significantly reduced the oxidation of the rocks and prevented uranium deposition in reservoir rocks This is likely the main reason of less common roll-front deposits type occurrences and low ore-grade uranium mineralization in the study area The chloritization, sericitization in sedimentary rocks under the impact of 3rd 4th deformation phases are also locally observed within the study area 4.5 Tectonic evolution of the northwestern part of Nong Son Basin 21 Based on the comparision of geological and deformation feature with recent study results, a tectonic evolution history of the region can be reconstructed with major stages (Figure 4.1) Figure 4.1 Summary of major geological events in the Nong Son Basin and adjacent area corresponding to regional tectonic events Stage 1: Formation of Neoproterozoic - Silurian active continental margin tectono-stratigraphic assemblages In this stage, the active continental margin tectono-stratigraphic assemblages were deposited within the study area, consisting of sedimentary, intrusive and volcanic rocks of the Kham Duc - Nui Vu Complex, A Vuong Formation and other intrusive/volcanic formations in southern and northwestern margin of the Nong Son Basin Stage 2: Silurian - Devonian orogeny In this stage, light color, S-type, syn-orogeny granite was widely formed and is an important uranium source supplying to subsequent Mesozoic sedimentary reservoir Most of the zircon grains accumulated in 22 sedimentary rocks of the An Diem Formation were dated as Late Silurian early Devonian age, corresponding to the S-Type granite surrounding the basin Many geologists reckoned that this type of magmatic rocks is and important uranium supplier to form such a redox or unconformable-type uranium deposits (Dahlkamp, 1994) Stage 3: Permo - Carboniferous active continental margin and Indosinian orogeny During the Carboniferous - Permian time, the study area was directly affected by the evolution of the Paleotethys ocean as consequence of Sibumasu - Indochina plate interaction, leading to formation of active continental margin magmatic rocks such as Ben Giang - Que Son Complex This regional collision resulted in 2nd deformation phase (B2), which completely folded previous structures of 1st deformation phase, in the mean time the Nong Son Basin had been destructed and geological formations have been deformed The last stage of the Nong Son Basin destruction was marked by the formation of a series of thrusted folding structure of the 2nd deformation phase Formation of the Nong Son Basin margin sedimentary rocks containing diverse sedimentary materials such as metamorphic fragments, S-type granite fragments, and volcanic fragments is an important source for uranium mineralization Meanwhile, deformation of these formations at the end of the 2nd deformation phase is an important premise for rock tilting and hence created comfortable for infiltration and migration of oxidation solution, leading to dissolving, accumulation and deposition of uranium in suitable environment in the study area Stage 4: Late Mesozoic - early Cenozoic post-orogeny intracontinental deformation In this stage, the subduction of plate systems has led to formation of a subduction zone and island arc volcano along eastern margin of this block and formation of the Cretaceous intrusive formation This is the cause of the 3rd deformation phaseaffecting the rocks in the region as the third deformation phase Due to faulting and folding process occurred in this deformed phase, attitude of the uranium reservoir rocks has been changed Stage 5: Cenozoic intra - continental deformation The 4th and 5th deformation phases are brittle deformation, creating fractures, faults, local displacement in the rocks under continental condition from the early Cenozoic to the present time This deformation phases have produced brittle fracturing zones with continuous block displacements, making pre-existing mineralization zones complicated and 23 hence the 3rd and 4th mineralization generation have been deposited in which the youngest uranium mineralization generation was dated at 14 Ma 4.6 The role of tectono-structure for uranium mineralization in sandstone of the northwestern part of Nong Son Basin 4.6.1 Overview of the uranium mineralization in sandstone The data derived from field investigation, composition analysis and uranium dating showed that in the study area, uranium mineralization is characterized by complex characteristics of attitude, morphology and temporal relation to surrounding rocks as summarized below: + Uranium ore has been formed in many generations, during a long period of time Results from uranium dating allowed me to define main stages of uranium mineralization in which the oldest stage was dated at 144 Ma while the youngest stage was at 17-14 Ma The datas on determination of stratigraphic age demonstrated that the youngest age of source rock is 221 Ma and is overlain by the Early Jurassic rocks It is clear that uranium ore are secondary genesis, which has been accumulated and has enriched in periods that are much latter than the timing of rock formation in the area + The timing of uranium mineralization generally was coincided with regional tectonic deformation, suggesting that regional structrures controlled uranium mineralization process The 1st uranium mineralization was started from the End of Jurassic and continued until Cretaceous, corresponding to latest stage of basin destruction and orogenic deformation Tectonic activities during the 2nd deformation phase forced sedimentary beds to tilt, intensfied fluid migration downward and uranium mineralization has gradually been occured in the study area + The next stages of uranium mineralization were also coincided with the 3rd,4th and 5th deformation phases It is demonstrated that tectonic movement directly affected rock attitude, constructed new structures resulted from deformation, complication and destruction of the previous ore bodies This process has also led to formation of a new ore generation that superposed on older mineralization or formed new ore bodies during fluid migration + Uranium has been dissolved, transported by the surface and underground oxidated fluid flow, deposited along the oxidation-reduction (redox) interfering zone, which were not completely depended on lithology of surrounding rocks 24 + Oxidation-reduction (redox) interfering zone has always migrated downward during ore forming process Formation or reactivation of broken and faulting zones provided comfortable conditions for oxidation fluid follow migration in different directions, especially along the fracture zones, leading to accumulation of new uranium-mineralized generation or destruction of previous mineralized zones under influence of the oxidation fluid flow 4.6.2 The role of tectonostructure controlling uranium mineralization in sandstone The tectonstructural elements have both positive and negative impacts on uranium mineralization in sandstone, they can be either a pathway/trap or destruction/down gradation of the pre-existing uranium mineralization prior to deformation 4.6.2.1 Mesozoic Basin opening process The pre-Mesozoic formations in the region include metamorphosed sedimentary, intrusive rocks derived from various sources, which have been deformed at different levels The Early-Middle Paleozoic formations and the olders were strongly affected by an orogenic deformation in the Middle Paleozoic, giving rise to folding, thrust faulting and subsequent uplift/exhumation of the older rocks, producing diversified sedimentary sources to the basin later Therefore, tectonics activities happened before Mesozoic Nong Son Basin formation has generated sedimentary sources for subsequent uranium mineralization 4.6.2.2 Mesozoic Nong Son sedimentary Basin formation The basin rifting activity has resulted in formation of a semi-enclosed basin connecting the sea that was prerequisite condition to produce an environment for sedimentary deposition and uranium mineralization Each type of this basin is characterized by typical environment, sediment composition, mineralization, morphology and size of ore body, uranium grade in ore bodies The regional rifting has led to formation of an intracontinental basin In which, the basin margin has been filled by sedimentary and acidic volcanic rocks of the Song Bung Formation This is a source rock supplying sediment material to the basin in the next stage of the basin evolution, including volcanic materials 25 4.6.2.3 Structures formed after the Nong Son Basin Formation The 2nd deformation phase resulted in production of reverse and thrusting zone, some folds in lower part of the Mesozoic formation were recorded in some place of the Nong Son Basin This phase triggered tilting of the rock layers, creating gentle dipping and fostering migration of oxidation fluid along rock layers, promoted formation of industrial uranium mineralization by redox mechanism The uranium dating data demonstrated that the first uranium generation has been occurred during the 2nd deformation phase This is the most important premises for uranium mineralization in this region However, these deformation phases have also given rise to disadvantageous elements for accumulation of uranium mineralization in the study area as addressed by the following factors: - The reverse and thrust faults have abruptly destructed and changed the attitude of rock formation Consequently, oxidating fluid flow was dispersed inside the rock formation and hence affecting the concentration of the uranium mineralization - Folding development during the 2nd deformation caused a change in dip angle of the rocks and therefore circulation of ore fluid and preservation of ore bodies have been changed The 3rd deformation phase is commonly characterized by various size folds and major faulting systems oriented in northeast-southwest and submeridian directions Formation of folds in this phase made a change in rock attitude or folding pre-existing ore bodies, while the development of faults in this phase triggered destruction of the ore bodies Deformation phases 4th and 5th has resulted in formation of broken and faulting zones oriented in northwwest-southeast, northeast-southwest and sub-parallel directions, dividing previous mineralized area into different blocks, making ore bodies complicated Tectonic destruction can be a pathway for oxidation fluid flow migration or secondary uranium deposition In summary, the results obtained from uranium mineralization studies show that uranium mineralization process in northwestern part of Nong Son Basin has been experienced stages, corresponding to regional tectonic deformation The aforementioned tectonic activities have significantly contributed to the explanation why the same tectonic and mineralization regime demonstrate different uranium potential 4.7 Establishing scientific basis for orientation of prospecting and exploration in sandstone of the study area uranium 26 4.7.1 Important premises and indicators for uranium prospecting in the study area 4.7.1.1 Lithology – rock facies premise - Favourable reservoir rocks - Presence of redox zone 4.7.1.2 Structural premise Tectonostuctural elements demonstrate both positive and negative influences on uranium mineralization process in sandstone of the study area They not only play a role of pathway or traps for uranium mineralization but also be preventing and/or destructing factors or reducing uranium grade in the previous mineralized units due to deformation process 4.7.1.3 Establishing prospecting indication - Geophysical anomalies - Geochemical anomalies - Outcrops and excavation works 4.7.2 Delineation of uranium potential areas in the study area 4.7.2.1 Principles of potential area delineation - Degree of uranium concentration - Details of research works 4.7.2.2 Standards for ppotential area delineation Based on the basis of prospecting premise, indications, details of research, potential delineation and standards, the areas was classified into different potential areas coded as A, B, C categories 4.7.2.3.Results on potential area delineation a A-category potential area This is a comfortable structure for mineralization, which was considered the most potential area It is necessary to carry out further investigation and exploration, including the whole Ta Bhing area b B-Category potential area This category consists of Ca Lieng - Suon Giua areas in the An Diem uranium ore region Because the area is situated near the uranium source 27 region, this structure is comfortable for underneath accumulation of uranium obove the oxidation-reduction barrier c C-Category potential area It is the remaining part of the lower An Diem sub-Formation, including A Vuong river confluent, Duoi, West An Diem, Khe Vinh areas, where There are searching premises such as relatively confortable structural elements and reservoir rocks, etc for uranium accumulation CONCLUSION AND RECOMMENDATION Conclusions Based on the above study results, the following conclusions can be made: Northwestern part of the Nong Son Basin is composed of Triassic and Early-to-Middle Jurassic coarse grained, molase sedimentary rocks overlying complex tectono-stratigraphic assemblages of Neoproterozoic Silurian active continental margin assemblage, Silurian-Devonian orogeny assemblage and Middle Carboniferous - Permian active continental assemblage Geological units in the Northwestern part of the Nong Son Basin have experienced at least tectonic deformation phases Each phase is characterizted by a group of structures formed in different temporal ans spatial domains The later deformation phase superposed the younger deformation phases leading to complex structural interference In which, the 2nd ÷ 5th deformation phases have affected Mesozoic sedimentary formations that infilled the basin, creating acomplicated structural grain These deformation phases play an important roll in controlling uranium mineralization prosess in the study area Uranium mineralization is ditributed in the coarse grained, fluvial and lacustrine sedimentary rocks along the margin of the basin, whose composition includes polymineralic gritty conglomerate, sandstone, or arkosic and grauvac sandstone intercalated by siltstone of the An Diem Formation (T3n ađ) Uranium mineralization was produced by oxidationreduction (redox) mechanism along the mixing redox front in the An Diem Formation Uranium mineralization in the study area was formed in periods, spanning from ca.144 to 14 Ma The oldest period of mineralization was dated at 144 Ma., corresponding to the Early Cretaceous, much younger than the age of the U-containing sedimentary rocks 28 The role of tectonostructural elements for uranium mineralization was illustrated by the basin opening process fostering deposition of sedimentary source for uranium mineralization and post-deposition deformation They not only play a role of creating favourable pathway and traps for uranium mineralization but also destructed or reduced uranium grade in mineralization zones Various uranium mineralization potential areas have been classified in order for orientation of geological/mineral survey, evaluation and exploration in the study region Recommendations It is necessary to have carry out detail studies on stratigraphy and sedimentary facies, clearly define the redox zone as well as to determine migration direction of the oxidation flow as the basin for prediction and delineation of the uranium ore bodies; A systematic interpretation to identify the existence, nature and the scale of folding-faulting structures containing mineralization in the region in order to determine the distribution pattern and destruction of the ore bodies is an essential task contributing to more accurate delineation of the uranium ore bodies and uranium resource estimation; Detail and systemetic survey on isotopic and geochemical properties of geological formations, which are likely the uranium source rocks such as intrusive and volcanic rocks, as well as the uranium mineralization and its distribution pattern are required to be conducted in order to accurately predict the uranium potential in the study area as well as in other parts of the Nong Son Basin The uranium potential areas should be comprehensively and integratedly evaluated interms of potential of uranium resouces by applying a combination of different methods for geological, structural, age dating, composition and particularly paleo-geographic and environmental purposes LIST OF SCIENTIFIC ARTICLES BY THE AUTHOR In Vietnamese: Nguyen Quang Hung, Nguyen Truong Giang, Nguyen Tuan Phong (1998), Some types of uranium mineralization in Nong Son basin Geological Magazine No 246, Ha Noi, p.26-30 Nguyen Quang Hung, Nguyen Truong Giang, Luu Van Dung (2000), Some types of mineralization, uranium mines in Vietnam Scientific conference at Ha Noi university of mining and geology 14th, Ha Noi, p.238-242 Trinh Dinh Huan, Nguyen Truong Giang va nnk (2013), Some types of uranium deposits are important in Vietnam Geological Magazine, series A, No 335, 5-6/2013, p.5-14 Nguyen Truong Giang, Nguyen Dac Son, Nguyen Dang Thanh va nnk (2013), Model of uranium mineral convergence in sandstone at Nong Son basin Geological Magazine, series A, No.335, 5-6/2013, p.15-29 Nguyen Truong Giang, Nguyen Dac Son va nnk (2013), Basis for selecting methods and networks for investigation and exploration of uranium ore in Nong Son basin Geological Magazine, series A, No.335, 56/2013, p.39-46 Nguyen Truong Giang, Tran Thanh Hai (2016) Magmatic intrusive complexes along the edge of Mezozoi Nong Son basin, central Vietnam and their regional significance Geological Magazine, series A, No.356, p.3749 Tran Thanh Hai, Bui Thi Men, Nguyen Quoc Hung, Nguyen Truong Giang(2016), Structural characteristics of the southeast part of Tam Ky Phuoc Son stitch section and its significance for the regional tectonic plan Geological Magazine, series A, so 356, p.07-18 Nguyen Van Lam, Nguyen Phuong, Tran Le Chau, Nguyen Truong Giang, Le Quyet Tam (2018), Some problems of creating uranium minerals in Nong Son basin sandstone Mining industry magazine, No.5 -2018, p.3035 In English: Piestrzynski, Tran Thanh Hai, Nguyen Truong Giang (2016) Timing of uranium mineralization from Mesozoic Nong Son Basin, Central Vietnam and its implication for regional sandstone-hosted uranium metallogeny; Proceedings of the 14th SGA Biennial Meeting: Mineral Resources to Discover, Quebec City, Canada; 2; 783-786 ... principles of uranium mineralization in sandstone 2.1.1 Uranium deposit models in sandstone 2.1.1.1 Overview of uranium deposits in sandstone Uranium deposits in sandstone are uranium accumulation,... surrounding the area 3.3.3 The age of uranium ore The first time in Vietnam an absolute age of the uranium ore has been dated In order to date the uranium, uranium ore samples within an ore body... on uranium have only focused on uranium potential in saperate areasand porposed orientation for porspecting and exploration works The researches on geological setting, tectonicstructure, uranium