TRƯỜNG ĐẠI HỌC MỎ ĐỊA CHẤT DOCTOR TRAN BINH CHU TIẾNG ANH CHUYÊN NGÀNH ĐỊA CHẤT (Dùng cho sinh viên ngành địa chất và địa chất mỏ) SPECIAL ENGLISH (FOR EXPLORATORY GEOLOGIST AND MINING GEOLOGIST) NHÀ XUẤT BẢN KHOA HỌC VÀ KỸ THUẬT HÀ NỘI TIẾNG ANH CHUYÊN NGÀNH ĐỊA CHẤT (Dùng cho sinh viên ngành địa chất và địa chất mỏ) Tác giả TRẦN BÌNH CHỮ Chịu trách thiện xuất bản PGS TS TÔ ĐÀNG HẢI Biên tập và sửa bài ThS NGUYỄN HUY TIẾN NGỌC DIỆP Trình bày bìa HƯƠNG LAN NHÀ XUẤT BẢN KHOA HỌC VÀ KỸ THUẬT 70 Tr.
CHAPTER ONE: MAJOR GENERAL INFORMATION
WHAT IS GEOLOGY?
Geology is the scientific study of Earth, encompassing its materials, processes, and history, including the evolution of life since its formation This discipline examines the physical forces acting on the planet, the chemistry of its components, and the biological evidence found in fossils Additionally, geologists investigate the Moon and other celestial bodies to uncover clues about Earth's origins, using this knowledge to assist in the discovery of valuable minerals within the Earth's crust.
MINERALS AND CRYSTALS
The Earth, Moon, and planets are composed of rocks made up of minerals, which are solid substances characterized by a regular and orderly arrangement of atoms This crystalline structure allows for the expression of a mineral's composition through a chemical formula.
Minerals grow freely and are defined by crystal faces that exhibit a consistent arrangement specific to each mineral species A crystal's naturally formed plane faces reflect its orderly atomic structure, resulting in a distinct outward shape.
Figure 1 Native elements: gold, silver and cupper
Figure 2 Minerals: chalcopyrite, sphalerite, wurtzite
Figure 3 Minerals: galena/galenite, pyrrhotine
MINERALS AGGREGATES
Most minerals exist as aggregates of crystals, which typically do not exhibit perfect shapes However, the aggregate's form can aid in identification For example, a structure resembling a cluster of grapes is known as botryoidal, while larger, rounded shapes are referred to as mamillated Native copper and gold can form unique branching patterns called dendritic Crystals that appear as flat sheets are categorized as lamellar, and if these sheets are very thin and easily separable, they are termed foliated These classifications, among others, are detailed in mineral descriptions.
ROCKS
Rocks, composed of minerals, make up the Earth, Moon, and planets, forming everything from towering mountains to sandy beaches Petrologists study these rocks not only to understand their mineral composition but also to decode the geological history they reveal By analyzing the record within rocks, significant insights have been gained regarding ancient climates, geographical changes, and the internal conditions of our planet.
Rocks can be categorized into three main types: igneous, metamorphic, and sedimentary Igneous rocks originate from the solidification of molten rock material, while metamorphic rocks arise from the transformation of existing igneous and sedimentary rocks Sedimentary rocks, on the other hand, are created through the accumulation of rock debris at the Earth's surface.
Revealed by fossils Được phát hiện bằng hoá thạch
Past inhabitance Đã sống/đã tồn tại
Extraterrestrial bodies Thiên thể các vật thể ngoài vũ trụ
Grow without constrain Phát triển tự do
Crystalline state Trạng thái tinh thể
Crystal faces Mặt tinh thể
Unravealed (adj) Không được phát hiện
Is bounded Được giới hạn
Petrologists Các nhà thạch học
Mineral aggregate Tập hợp khoáng vật
Solid substances Các chất rắn
Dendritic (adj) Dạng cành cây
To unravel Làm sáng tỏ
‘Record of the rocks' Di tích, tài liệu của đá
Igneous rocks Đá macma xâm nhập
Metamorphic rocks Đá biến chất
Sedimentary rocks Đá trầm tích
WHAT IS EXPLORATION?
In North America the terms “Prospecting & Exploration” are interchangeable with
Exploration encompasses the complete process of identifying potential mining sites, starting with reconnaissance to locate prospects, followed by evaluating these prospects, and ultimately searching for additional ore within a mine.
In Russia, "prospecting for mineral deposits" and "exploration" are terms used to describe the process of examining mineral deposits after their discovery (Kreiter 1968, p 114) Conversely, in France and several other countries, "exploration" denotes a broad search for signs of mineralization, while "prospecting" is focused on a more localized investigation of these indications (Routhier, 1963, p 1002).
PRINCIPLE STEPS IN THE ESTABLISHMENT & OPERATION OF A
1 Mineral exploration: To discover an ore-body
2 Feasibility study: To prove its commercial viability,
3 Mine development: Establishment of the entire infrastructure
4 Mining: Extraction of ore from the ground
5 Orc dressing (mineral processing): Milling of the ore, separation of ore minerals from gangue, separation of the ore minerals into concentrates, separation & refinement of industrial mineral products
6 Smelting: Recovering metals from the mineral concentrates
8 Marketing: Shipping the products to the buyer (Custom smelter, manufacturer).
SPECIALISTIC TERMS
1 Economic geology: A study the geological aspects (including age, genesis, environment of formation, grade and grade distribution, tonnage, mineral paragenisis, geochemistry, etc ) of the mineral resources in this Earths crust
2 Mineral deposit: A natural concentration of useful substances, which under favourable circumstances can be profitably extracted; or a rock building association from which under the prevailing technical and economic condition, one or more metals or compounds may be profitably extracted Or in other words: the natural occurring material from which a mineral or minerals of economic value can be extracted
3 Mineralization: (i) The process by which matter is introduced into a rock resulting in the formation of new minerals of potentially economic value or of a mineral deposit; (ii) The state resulting from this process
4 Resource: A natural concentration occurring solid, liquid, or gaseous materials in or on the Earths crust in such form that economic extraction of a commodity is currently or potentially feasible
5 Reserve: Thai portion of the identified resource from which a usable mineral or energy commodity can be economically and legally extracted at the time of determination (Figure 6)
Prospecting & Exploration Tìm kiếm và thăm dò
Reconnaissance Khảo sát, điều tra
Refining Tinh chế, luyện tinh
Gangue mineral Khoáng vật mạch, không quặng
Mineral deposit Mỏ khoáng, mỏ khoáng sản
Profitably extracted Khai thác có lãi
Mineral Resource Tài nguyên khoáng sản
Mineral Reserve Trữ lượng khoáng sản
Potentially economic value Có giá trị kinh tế tiềm năng
Figure 6 Evoluation of resources to reserves (Modified from Hughes et al 1988, according to scheme proposed by Harrison 1983)
CHAPTER TWO: GENERAL GEOLOGY
GEOLOGICAL MAPS
Topographic maps depict the Earth's surface features and may include various natural and artificial elements for informational purposes When learned to read effectively, these maps serve as valuable navigational tools.
Geological maps are essential tools for illustrating the underlying geology of an area, with bedrock geology maps being the most prevalent type These maps depict the geological formations as they would appear without soil cover, allowing for insights into subsurface structures Additionally, there are various geological maps that highlight the distribution of soil types, glacial deposits, and other surface geological features.
Creating a geological map begins with the crucial step of identifying a suitable set of map units, which can include individual sedimentary rock formations, distinguishable lava flows, or metamorphic rock units By pinpointing the specific map units present at each location where rocks are exposed, geologists can effectively chart the geological landscape.
In geological mapping, it's important to document additional details like the orientation of beds and the locations of contacts between different map units Clear contacts are represented by solid lines, while inferred contacts are indicated by dashed lines.
Geological maps utilize color coding to clearly distinguish different units, often displaying similar-aged units in varying shades of the same color Each map is accompanied by a chronological key, listing units from youngest to oldest, along with brief descriptions or standard patterns indicating the general rock type Additionally, every unit is assigned a symbol, starting with one or two letters that represent the unit's age system (period), followed by one to three lowercase letters denoting the series (epoch).
Geological maps frequently include markers that aid readers by providing geological cross sections, which represent a three-dimensional view of the surface geology The specific line along which these cross sections are drawn is clearly indicated on the map, utilizing the same map units and symbols for consistency.
18 map proper and attempts to show the geometric relationships inferred to exist among those units- fauls, folds, intrusive relationships, and so on (Figures 7, 8, 9)
A cross section is created by establishing a topographic profile along a selected line and depicting the surface geology The ability to develop a definitive structural interpretation of the geological map depends on the complexity of the geology and the extent of the surface exposure In cases where a unique interpretation is not feasible, multiple plausible alternatives may be offered Cross sections play a crucial role in assessing site suitability for mineral exploration, construction, and various other applications.
Figure 7 Geological map of the Stanthorpe Tinfield
Figure 8 Geological map of Blue Tiger Tinfield
Figure 9 Geological plan at R.L 10 ft of the King Island scheelite deposit
Topographic map Bản đồ địa hình
Geological map Bản đồ địa chất
Subsurface structure Cấu trúc dưới mặt đất, dưới sâu
Be deducted Bị giảm đi
Rocks are exposed Đá lộ ra
Chronological order Theo thứ tự tuổi
Be assigned Được gán cho
Geological cross sections Mặt cắt địa chất
Thre-dimensional interpretation Giải thích trong không gian ba chiều
Fauls: folds Đứt gãy; nếp uốn
Unique (adj) Duy nhất/dị thường
Plausible alternatives Biến đổi hợp lý/logic
Mineral exploration Thăm dò khoáng sản
LITHOSPHERE
The Earth's lithosphere, a rigid stony layer averaging 100 kilometers in thickness, covers a molten mass known as magma, which is believed to extend over 1,000 kilometers deep Beneath the magma lies the Earth's core, primarily composed of iron, nickel, and other metals, contributing to the planet's significant weight and magnetic properties Some metals from the core seep into the magma, which then moves through fissures in the Earth's crust, cooling slowly to form "veins" that give rise to various ores and metals The abundance of magmatic veins correlates with the number of ore deposits, with the richest reserves located in the lower strata of the lithosphere The majority of the Earth's surface is covered by water, with land emerging as continents and islands of varying sizes.
The Earth's hydrosphere is comprised of rivers, lakes, swamps, groundwater, and glaciers, creating a dense network of water that envelops the lithosphere Above this water cover lies the atmosphere, which serves as the final layer surrounding the planet and extends approximately 500 kilometers in thickness.
THE STRUCTURE OF THE EARTH'S CRUST
The Earth's crust is a thin layer, akin to the skin of an orange, varying in thickness with the thickest areas found beneath mountains and the thinnest under ocean basins This layer contains essential materials utilized by humans, such as oil, copper, and gold The hydrosphere refers to the liquid portion of the crust, encompassing all the Earth's water, while the solid part, known as the lithosphere, is made up of rocks and minerals.
There are three types of rocks: metamorphic, sedimentary and igneous
Metamorphic and sedimentary rocks are organized in strata, with the oldest layers located at the bottom and the youngest at the top In contrast, igneous rocks typically intrude through these strata, making them younger than the surrounding rock layers.
The Earth's crust has an average thickness of about 100 kilometers, yet the deepest drilling only reaches 2 to 2.5 kilometers Despite this limitation, researchers have developed methods to study the lithosphere at greater depths For instance, in broken mountain ranges, limestone layers can be observed at depths of 4 to 5 kilometers, while similar layers are also visible at the surface.
Dolomite layers found at depths of 6 to 7 kilometers are also exposed at the surface As mountains age, they undergo significant erosion from environmental elements, revealing deeper lithospheric strata across extensive distances, often spanning scores of kilometers.
In search of minerals man has been studying mountains with a great attention As a result we have now a rather clear picture of the internal structure of the Earth's crust
Water easily transports soft rocks like clay, sand, and gravel, with quick streams capable of carrying larger stones As the stream slows, larger particles settle at the bottom, and when it reaches a plain or lake, the flow halts completely This results in the accumulation of sediments, including clay, sand, and fine silt, which settle in even horizontal layers.
The lithosphere's surface primarily features soft stones such as clay and sand, which are typically found in strata formed by precipitation from water In certain instances, these soft stones can also be deposited by air, as seen in desert environments where dust and fine sand accumulate Collectively, rocks formed through these processes are classified as sedimentary rocks.
Sedimentary rocks form when layers of sand, clay, and other soft materials are compressed by overlying strata The weight of these upper layers compresses the lower strata, while infiltrating waters introduce mineral solutions that cement the soft rocks into harder formations This process transforms clay into loamy schists, sand into sandstone, gravel into conglomerate, and organic materials into coal, along with limestone from precipitated sea shells.
Sandstone and loamy schists frequently reveal fossilized traces of leaves, shells, fish, and other aquatic creatures, indicating that these geological layers were formed by sedimentation in water long ago.
Sedimentary rocks create a layer on the Earth's crust, covering approximately 75% of continental regions and the majority of the ocean floor These rocks can reach thicknesses of up to 10 kilometers, yet they account for only about 5% of the Earth's crust.
Sedimentary rocks primarily originate from the weathering of existing rocks, with the rate of denudation playing a crucial role in determining sediment production and its characteristics This denudation process is cyclical, with each erosion cycle leading to a corresponding sedimentation cycle Additionally, geological structures significantly impact the breakdown rate of rocks, while the volume of sedimentation is influenced by the degree of subsidence in deposition basins.
Sedimentary rocks are primarily formed from particles that have experienced different degrees of transportation To transform loose sediment into solid rock, a process called lithification is necessary, which includes consolidation and cementation The effectiveness of lithification is influenced by the sediment's composition, texture, and the pressure exerted by the overburden.
The texture of sedimentary rocks is determined by the size, shape, and arrangement of their constituent particles Due to their small size, sand and silt grains must be measured using sieving and sedimentation techniques, while individual clay particles require an electron microscope for measurement The results of these size analyses can be represented graphically, often using frequency histograms or cumulative curves to illustrate the data effectively.
Certain sedimentary rocks are the products of chemical or biochemical precipitation whilst others of organic origin Thus, the sedimentary rocks can be divided into two principal groups:
1 Clastic or exogentic types: and
2 Non-clastic or endogenetic types
However, one factor which all sedimentary rocks have in common is that they are deposited and this gives rise to their most noteworthy characteristic, i.e they are bedded or stratified
Gravel is an unconsolidated collection of rounded fragments, which, when indurated, transforms into conglomerate Sands are composed of a loose mixture of mineral grains and rock fragments, and their conversion into sandstone involves mechanical processes such as grain fracturing, bending, and deformation Siltstones can be either massive or laminated, while clay deposits primarily consist of fine quartz and clay minerals Limestone is defined as rocks containing more than 50% carbonate, predominantly in the form of calcite or aragonite.
Shale is the most prevalent type of sedimentary rock, known for its distinctive lamination In contrast, sedimentary rocks that share a similar size and composition but lack lamination are typically classified as mudstone Additionally, peat deposits form in poorly drained areas, where the presence of humic acid leads to deoxygenated conditions.
TEMPERATURE OF THE EARTH
The Earth's surface receives heat primarily from the Sun, but this warmth does not extend deeply into the ground Observations reveal that at depths of 20 to 30 meters, temperatures remain consistent throughout the year, unaffected by seasonal changes However, temperatures begin to vary significantly when digging deeper than this range.
Over a depth of 30 meters, it is observed that the Earth's temperature consistently rises Various studies conducted during the excavation of shafts, tunnels, and borings indicate that for every 33 meters of depth, there is an increase in temperature of approximately 1 degree Celsius.
Based on our calculations, the Earth's temperature varies with depth; for instance, at 30 meters, the temperature is approximately 5°C, while at 500 meters, it rises to about 19-20°C, and at 1000 meters, it reaches around 40°C.
Recent observations support our calculations, particularly from a deep borehole reaching 2,440 meters in the Upper Silosia, where a temperature of 83°C was recorded at 2,220 meters While these findings pertain to the upper layers of the lithosphere, evidence suggests that temperatures continue to rise with depth This is further validated by the presence of hot springs and volcanic activity, which emit molten lava at significantly higher temperatures.
FORMATION OF MOUNTAINS
The Earth's crust undergoes significant shifts in some areas, resulting in the formation of mountains through the bending, folding, and cracking of its layers This process creates distinct rock strata contours in mountainous regions, often characterized by folds of various sizes and shapes, as well as deep transversal cracks known as faults Folded mountains, such as the Caucasus, Alps, and Himalayas, are formed when numerous folds are present, while faulted mountains, like the Transbaikal and Juguli Mountains, are shaped primarily by faults.
Cracks and fissures in the Earth's crust can extend deep enough to reach the magma layer, allowing molten substances to rise and emerge at the surface This process leads to volcanic activity, as these outlets of melted materials create various volcanic phenomena.
VOLCANISM
Volcanoes are mountains formed by the eruption of gases, molten rock, and blazing stones from deep within the Earth The opening through which this volcanic material is expelled is known as a crater.
Lava thickness can vary significantly, and when it becomes very thick, it hardens within the volcano's crater, leading to a blockage This buildup causes gases to accumulate, which, when released, can explosively shatter the hardened lava into fine volcanic ash.
Volcanic eruptions can vary significantly based on the state of the lava When large explosions occur, volcanic bombs are ejected from the crater, while liquid lava flows smoothly down the slopes without explosive force The type of eruption not only influences the eruption's character but also affects the volcano's external appearance Volcanoes that erupt hardened lava, consisting of stones and ash, often resemble a sand pile with a flattened top In contrast, those that erupt liquid lava develop slanted slopes, giving them a flatter appearance from a distance.
Volcanic eruptions create a terrifying spectacle, characterized by towering columns of burning gases, steam, and thick clouds of volcanic ash Incandescent stones are ejected alongside the ash, accompanied by a deafening rumble from beneath the Earth's surface Often, storms develop as thick clouds gather, resulting in rain mixed with ash that falls like hot dirt Entire towns, such as Herculaneum, Pompeii, and Stabia, have been buried under layers of ash and lava, with their ruins now excavated near Naples, Italy In 1902, the eruption of a volcano devastated the American city of San Sierre, claiming the lives of over 4,000 residents.
Kamchatka is home to over thirty volcanoes, including the towering Kluchevskaya volcano, which stands at 4,816 meters, making it one of the highest volcanoes in the world The region showcases a fascinating landscape where ancient volcanic lava has cooled over thousands of years, yet steam and boiling water continue to emerge from cracks in the hardened lava, giving rise to numerous geysers and hot springs In addition to the active volcanoes, Kamchatka features many extinct volcanoes, which can also be found in the Caucasus and Transbaikal regions.
Massive rocks are formed from the cooling of molten liquid masses When this cooling occurs rapidly at the surface, it results in non-crystalline rocks, commonly known as lava Conversely, when cooling takes place deep within the lithosphere, crystalline rocks are produced.
Granite formation occurs when molten rock cools slowly under high pressure, resulting in the development of large crystals, known as coarse-grain granite In contrast, rapid cooling produces fine crystalline rocks, with larger crystals found deeper within the Earth's crust This slow cooling process is essential for the formation of ore deposits, which are more abundant in the lower strata of the lithosphere compared to the upper layers, where quick cooling prevents ore formation.
PERPETUAL ROCKING OF THE DRY LAND
The continuous destruction of mountains leads to the movement of materials such as clay, sand, and stones to lower areas, gradually lowering the mountains over thousands of years As erosion occurs, the mountainous regions experience a slow rise, while in the low-lying areas, the accumulation of sediments increases weight, causing these regions to gradually sink into the magma below These processes of rising and sinking are prevalent on the Earth's surface, though they occur so slowly that they are imperceptible to the naked eye.
Near Naples on the Apennine Peninsula, ancient temple ruins can be found along the shoreline, originally constructed over 2000 years ago Due to gradual sinking, the shore has descended twelve meters over the past 1200 years, resulting in the temple becoming submerged However, the temple has since risen six meters, although its foundation remains underwater.
Changes in the landscape occur gradually, as illustrated by marks cut into granite rocks along the Gulf of Finland about 200 years ago Today, these marks are positioned two meters higher than their original placement, indicating that the area is rising at a rate of one meter every century.
Evidence of significant geological changes in the Earth's crust is demonstrated by the presence of extensive layers of pelagic sediments, including chalk and limestone, found on dry land These sedimentary rocks account for more than two-thirds of the Earth's terrestrial surface.
VOLCANISM AND FISSURES IN THE EARTH'S CRUST
Explorations have shown that volcanoes are present only where there are deep cracks in the Earth's crust The majority of cracks are situated on the shores of the Pacific -
28 the Great Ocean making what is called the Pacific Volcanic Ring Here we also find the majority of volcanoes Altogether there are about 400 volcanoes in the world and
There are approximately 300 volcanoes located near the Pacific Ocean, forming long rows along the shores of the Asian and American continents and various islands, including the Kamchatka, Philippines, and Sunda regions Many of these volcanoes emerge directly from the sea floor, creating chains such as the Kuril Islands, along with numerous other small Pacific islands Additionally, volcanoes can be found scattered across islands in the Mediterranean and Caribbean Seas.
Magma beneath the Earth's crust can ascend through fissures due to the immense pressure exerted by the crust above This phenomenon is similar to water rising in a hole during winter when ice compresses it As magma rises, it heats and melts the surrounding walls of the cracks, leading to the accumulation of significant amounts of gas and steam These gases, lacking an outlet, become partially dissolved in the magma and partially collect at the tops of the cracks.
METAMORPHISM AND METAMORPHIC ROCKS
Metamorphic rocks originate from existing rock types that have experienced significant mineralogical, textural, and structural alterations due to changes in their physical and chemical environments These transformations occur in a solid state, driven primarily by variations in temperature and pressure, which initiate metamorphic reactions Each mineral remains stable within specific temperature and pressure limits; exceeding these thresholds necessitates mineralogical adjustments to achieve equilibrium with the new conditions The term "grade" is used to describe the temperature range during which metamorphism takes place.
Metamorphism typically results in minimal changes to the bulk composition of rocks, primarily affecting water and volatile components like carbon dioxide; this process is known as isochemical change In contrast, allochemical changes occur through metasomatic processes that involve the introduction or removal of materials from the affected rocks These metasomatic changes are driven by hot gases or solutions that permeate through the rock formations.
Metamorphism can be broadly classified into two main types based on geological settings, namely thermal or contact metamorphism and regional metamorphism These processes result in the formation of various metamorphic rocks, including quartzite, marble, and slate, as well as quartz schist, gneiss, granulite, amphibolite, and green schist, each with distinct characteristics and textures shaped by intense heat, pressure, and chemical reactions.
Lithosphere Quyển đá, thạch quyển
Hydrosphere Quyển nước, thủy quyển
Explore (v) Thăm dò, khảo sát
Internal structure Cấu trúc bên trong
Sediments Vật liệu trầm tích
Sedimentary rock Đá trầm tích
Sedimentary stone Đá trầm tích
Loamy schist Đá phiến sét
Filtration water Nước thấm lọc
Massive rocks Đá kết tinh dạng khối
Melted liquid masses Vật chất nóng chảy, dung thể macma
Crystalline rocks Đá kết tinh
Ore deposits Các mỏ quặng
Melted liquid magma Dung thể macma nóng chảy
Eroded mountainous place Vùng núi xâm thực
To plunge into magma Chuyển thành macma, nhấn chìm vào macma
To begin to rise again Bắt đầu tải nâng lên
Has risen already Đã nâng lên
Pelagic sediments Trầm tích biển
Pelagic origin Nguồn gốc biển
Volcanism Hoạt động núi lửa
To blaze Sáng chói, mãnh liệt
External appearance of the volcano Biểu hiện bên ngoài của núi lửa
To descend on Rơi xuống
Enormous To lớn, khổng lồ
Hot spring Suối nước nóng
The acting volcanoes Núi lửa đang hoạt động
Extinct volcanoes Núi lửa đã tắt
To undergo Trải qua, chịu, bị
To shift Dịch chuyển, trượt
To be gathered into folds Tạo thành nếp uốn
Folded mountains Núi uốn nếp
To predominate Trội hơn, chiếm ưu thế
Faulted mountains Núi đoạn tăng
Fissures Khe nứt, đứt gãy
Outlets Sự trào, sự dâng lên
To emerge Trào ra, dâng lên, phun lên
Exploration Sự khảo sát, sự tham dò
Volcanic ring Cung núi lửa
To make chains Tạo nên các chuỗi, dãy mắt xích
To be scattered Rải rác
Mediterranean Sea Địa Trung Hải
Great quantities Một số lượng rất lớn
Perpetual rocking Sự tạo đá liên tục
Emerge at the surface Trào lên mặt đất, phun trào
Sedimentary rock Đá trầm tích
An outer skin Một lớp mỏng
Covering three-quarters Phủ ba phần tư
Denudation Bóc mòn, mài mòn
Cyclic process Quá trình có tính chu kỳ
Cycle of erosion Chu kỳ xâm thực, bóc mòn
Basin of deposition Bể bổn trầm tích
Must be lithified Trở thành đá
Size, shape and arrangement of Hình dạng, kích thước và sự sắp xếp của
To be measured in directly by sieving Có thể đo trực tiếp bằng tay, sảng
An electron microscope Kính hiển vi điện tử
To draw cumulative curve Vẽ đường cong luỹ tích
Noteworthy (adj) Đáng chú ý/ đáng ghi nhớ
Bedded or stratified Phân lớp phân tầng
Metamorphic rocks Đá biến chất
Progressive transformations Biến chất tiến triển
Establish equilibrium Thiết lập sự cân bằng
Volatile constituents Thành phần khí
Isochemical changes Biến đổi đẳng hoá
Allochemical changes Biến đổi phi đẳng hoá
Geological setting Bối cảnh địa chất
Green schist Đá phiến màu lục
Quartz schist Đá phiến thạch anh
Marble Đá hoa/đá cẩm thạch
THE NATURE OF THE EARTH'S CRUST
The Earth's crust is the rigid and generally brittle outer layer situated above the Mohorovičić discontinuity (Moho) Our understanding of the crust's characteristics has primarily been shaped by geophysical measurements, particularly seismic and gravity data, alongside insights gained from high-pressure and high-temperature laboratory experiments This knowledge is further supplemented by surface observations and materials obtained through geological processes like volcanic activity, deep faulting, and extensive drilling programs.
The Earth's crust can be divided conveniently in two readily distinguished crustal types- continental crust and ocenic crust, and both types will be examined seraparately
Seismic velocity variations with depth indicate changes in crustal chemistry or mineralogy, influenced by increasing pressure from lithostatic forces Temperature rises at an average rate of 25°C/km above the Moho but decreases to about half that rate below due to the lack of radioactive heat sources The uppermost crust is characterized by surface and near-surface activities, such as erosion, sedimentation, and volcanism.
The average crustal density of around 2.77 - 2.82 is significant higher than that of granite (2.67) The actual average crustal density corresponds to a rock type somewhere between grnodirite and diorite in composion
Crustal thickening through fold and faul induced lateralcrustal shortening and vertical thrust stacking are resonable and demonstrable mechanism
Some 12 divisions are recognised on the basis continental of ocenic affinity, relative stability, morphology and structure They are the following: shiels, platforms, Paleozoic orogenic belt, Mesozoic-Cenozoic orogenic belt, continental rift system, volcanic island, island-arc, trench, ocean basin, oceanic ridge, marginal-sea basin, inland-sea basin
Seismic studies cofirm that the oceanic crust is very thincomperad to continental crust
(6 - 7 km beneath an avegage water depth of 4.5 km) It may be divided into three discernible layers (Figures 11, 12):
- Oceanic Layer 1: These deep sea sediments, average thicness is 0.4 km
- Oceanic Layer 2: These layer is igneous in origin and is dominated by tholietic olivine basalts with pillow lavas a dominant feature Layer 2 is variable in thickness, ranging from 1.0 to 2.5 km
Oceanic Layer 3 is a crucial part of the oceanic crust, serving as its plutonic foundation This layer can be further divided into two sub-layers, with the upper layer primarily composed of gabbro and featuring some pockets of plagiogranite.
Figure 10 Schematic cross section through continental crust
The lower sub-layer of the Earth's crust is composed of cumulate gabbro and ultrabasic rocks, which may undergo serpentinization at depth due to crystal settling Plate tectonic theory posits a rigid system of crustal plates whose movements, driven by the Earth's internal heat, are evident at their boundaries These boundaries are sites of significant tectonic processes and events, characterized by consuming, translational, or extensional interactions, leading to distinct geological features Additionally, it is common to find stable configurations involving two or more plates over extended periods.
Plate boundaries are classified into three main types: ridges, trenches, and transforms Ridges represent divergent boundaries where new crust is formed, while trenches are convergent boundaries where existing crust is consumed In contrast, transform boundaries involve lateral movement of the lithosphere, conserving rather than creating or destroying crust.
Figure 11 Generalized cross-sections of continental crust based on exposed section of deep crustal rocks
The P and S wave velocity structure of the oceanic crust is analyzed through layered models established in 1965 and 1978, with velocities measured in kilometers per second The dashed curve illustrates a gradual increase in velocity with depth, as referenced in studies by Spudith and Orcultt (1980) and Harrison & Bonati (1989).
Britle outer layer Lớp vỏ cứng ngoài cùng
Earth's crustal character Đặc tính của vỏ trái đất
Interpreting geophysical measuments Giải thích tài liệu địa vật lý
Continental crust and ocenic crust Vỏ lục địa và vỏ đại dương
Seismic velocities Tốc độ địa chấn
Lithostatic forces Áp lực thuỷ tinh
Radioactivive heat sources Nguồn năng lượng phóng xạ
Stacking adj Chất đồng, chồng chất
Orogenic belt Đại tạo núi
Volcanic island Đảo núi lửa
Island-arc, french Cung đảo, vực biển
Occanic ridge Sống núi đại dương
Marginal-sea basin Trũng biển rìa
Inland-sea basin Trùng biển nội lục
Discernible Có thể nhận thức rõ, thấy rõ
Pillow lavas Dung nham dạng gói
Cumulate gabbro Gabro dồn tích
Ultrabasic rock Đá siêu mafic
Rigid system Hệ thống cứng
Crustal plates Màng vỏ trái đất
Manifest Hiển nhiên, rõ ràng
Consuming plate Mirg hút chìm/ mảng chúc xuống
Extensional plate Mảng tách giảm căng giãn
Stable configurations Cấu hình bình ổn
Pricipal tenant Vùng đất chính
Transforms Dịch chuyển/ Dịch trượt
Ridges Dãy núi/ Sống núi đại dương
Trenches Vực biển, hẻm vực
Divergent plate boundaries Ranh giới mảng tách giãn
Covergent plate boundaries Ranh giới mảng hội tụ
Slip plate boundaries Ranh giới mảng dịch trượt
Is consumed Bị hút chìm? Bị chúc xuống
CHAPTER THREE: ENDOGENETIC MINERAL DEPOSITS
DEPOSITS RELATED TO MAFIC IGNEOUS ROCKS
This chapter focuses on deposits related to mafic rocks, which encompass some of the largest igneous petrologic systems globally, such as the Bushveld Complex, as well as moderate-sized bodies like carbonatites The ore minerals found within these systems are integral components of the igneous rocks themselves Understanding these relationships underscores the importance of economic geology, a subdiscipline that applies petrologic tools and methodologies to address issues traditionally explored by general economic geologists The discussion emphasizes the significance of thin-section petrology, polished-surface mineralogy, and geochemistry, highlighting that a comprehensive understanding of specific minerals like chromite requires considering the genesis of the associated rocks Consequently, the scope of analysis expands to encompass entire ore-forming petrologic systems.
Ore deposits resulting from the fractional crystallization of magmas were identified prior to Lindgren's classification system, as noted by Vogt in 1984 These deposits, referred to as magmatic segregation deposits, are defined as direct crystallization products of magma, excluding pegmatites, porphyry base-metal deposits, and those involving hydrothermal transport Typically formed within magma chambers, these deep-seated intrusive bodies can also result from differentiated or immiscible melts and crystal mushes that are driven into the walls or roofs of magma chambers, leading to the formation of orebodies such as dikes, sills, and even extrusive flows.
Magmatic segregation deposits can form entire intrusive rock masses or distinct compositional layers within them, characterized by valuable accessory minerals in otherwise typical igneous rocks The ore minerals may originate from early or late fractionation processes, concentrated through mechanisms like gravitational settling of crystals or liquids, liquid immiscibility, or filter pressing These minerals can either remain in situ or be injected as ore magma into solidified plutons or surrounding country rock The separation of immiscible magmatic liquids, such as sulfides, plays a crucial role in this process.
The significance of oxide liquids derived from silicate melts in magmatic segregation and ore formation has been highlighted by several researchers, including Fischer (1950), Hawley (1962), McDonald (1967), Philpotts (1967), MacLean (1969), and MacLean and Schimazaki (1976) Fischer and Philpotts focused on magnetite-apatite fluids as immiscible components of silicate melts, while MacLean explored the immiscibility of silicate-sulfide liquids.
Figure 13 Deposit related to ultramafic/ mafic intrusive
Certain ore minerals are typically associated with specific types of igneous rocks; for instance, mafic rocks commonly contain chromite, ilmenite, apatite, diamond, nickel, copper, and platinum group elements In contrast, igneous rocks of intermediate composition are often associated with magnetite, hematite, and accessory minerals like zircon, monazite, uraninite, and cassiterite Notably, some associations are more restrictive, such as chromite, which is closely linked to peridotite, dunite, or serpentine derived from ultramafic rocks found in Alpine peridotite deposits This tendency for specific ore-host-rock associations supports the concept of magmatic segregation as a significant ore-forming process The deposits discussed in this chapter are primarily part of the mafic and ultramafic sections of igneous rock systems and are typically found within cratonic masses or continental crust, encompassing some of the largest ore-forming magnetic systems known.
The world is home to 39 notable layered mafic intrusions (LMI), with the most recognized examples being the Bushveld Igneous Complex in South Africa, the Great Dyke in Zimbabwe, the Sudbury Complex in Canada, as well as the Stillwater and Duluth complexes in the United States.
Figure 14 Schematic cross – sections through plate boundary – relates tectonic settings of mineralizion (from Michell & Garson, 1976)
Deposits related to mafic Igneous rocks Các mỏ liên quan với đá macma mafic
To be hosted Được vây quanh bởi, được
Ore forming systems Hệ (chứa quặng) tạo quặng
Magnetic aggregation deposit Mỏ macma phân tụ mỏ macma thực sự Pegmatile pecmatit
Porphyry base-metal deposits Các mỏ kim loại cơ bản nguồn gốc pocphia Hydrothermal transport Sự vận chuyển của dung dịch nhiệt dịch
Deep-seated intrusive bodies Các thể xâm nhập sâu
Polished-surface mineragraphy Khoáng tướng
Immiscible Không trộn lẫn, đồng nhất
Crystal mushes Dung thể kết ting
Dikes Thể đai cơ thể tường)
Sills Thể vỉa xâm nhập
Extrusive flows Dòng phun trào
Entire intrusive rock mass Toàn bộ khối macma xâm nhập
Single compositional layer Lớp hay via cấu thành của khối xâm nhập Valuable accessory minerals Các khoáng vật phụ có ích
Early fraction product Sản phẩm phản dị (kết tinh sớm
Late fraction product Sản phẩm phản dị (kết tinh) muộn
To be concentrated by gravitate settling Được tập trung do lắng đọng trọng lực (hay tích tụ do lắng đọng trong trọng lực)
To be injected into Được tiêm nhập vào
Ore magma Macma chứa quặng
Solidified Pluton The pluton đã đông cứng (thế xâm nhập sâu đã đông cứng)
Silicate melt Dung thể silicát nóng chảy
Silicate-sulfide liquid invisibility Tính chất không trộn lẫn của dung dụng thể silicat và dung thể sunfua Consistent affiliations Các mối liên kết vững chắc
Platinum group elements Các nguyên tố nhóm bạch kim
Ultramafic rocks Các đá siêu mafic
The ore-host-rock association refers to the relationship between mineral deposits and the surrounding host rocks, highlighting the interplay between ore minerals and their geological context Magmatic aggregation serves as a crucial ore-forming process, where the differentiation of magma leads to the concentration of valuable minerals, ultimately resulting in the formation of ore deposits Understanding these associations and processes is essential for effective mineral exploration and extraction.
Mafic portion Phần mafic, hợp phần mafic
Igneous rock systems Các hệ thống các lớp) đá macma xâm nhập
To be logded in Được lắng đọng ở; được định vị ở
Carbonic masses Các khối địa khiên
Continental crust Vo luc dia
Oceanic crust Vỏ đại dương
Layered mafic intrusions Các thể xâm nhập mafic dạng via, sự xâm nhập mafic dạng lớp
Igneous complex Phức hệ đá xâm nhập
To be bring found and explored Đang được tìm kiếm và thăm dò
Igneous intrusions often lead to significant changes in surrounding rocks, which can undergo recrystallization, alteration, mineralization, and replacement, particularly at the contact zone These transformations, driven by heat and fluids associated with the intrusions, are collectively referred to as igneous metamorphism, pyrometamorphism, and pyrometasomatism.
Contact metamorphism encompasses various terms, including igneous metamorphism, which is favored by many geologists due to its broader definition Pyrometamorphism specifically addresses thermal effects and replacement activities near igneous contacts, although significant metamorphic deposits can exist far from intrusive massifs This term can also describe alteration assemblages with skarn minerals found at contacts or along veins, without necessarily indicating high-temperature, high-pressure conditions While igneous metamorphism covers all alteration forms linked to igneous rock intrusion, it may not fully capture the dominant metasomatic effects present in certain deposits Therefore, Einaudi (1982) suggested adopting the non-genetic term "skarn" for more accurate classification.
Skarn is a historical Swedish mining term that refers to silicate gangue, including minerals such as amphibole, pyroxene, and garnet, found in certain Archaean iron and sulfide deposits, particularly those that have replaced limestone and dolomite Over time, the definition has broadened to encompass lime-bearing silicates of any geological age, which are derived from nearly pure limestone and dolomite and are characterized by significant amounts of silicon, aluminum, iron, and magnesium.
Contact metamorphic aureoles surrounding igneous bodies are characterized by the formation of fine-grained rocks known as hornfelses, resulting from an isochemical process where significant matter transport is minimal In cases where the country rock contains reactive minerals like calcite, dolomite, and argillaceous minerals, coarser-grained skarn may develop Metasomatic changes can occur when volatile compounds and metal ions emanating from the igneous body interact with the surrounding rocks; however, substantial matter transport is only feasible in an open system, facilitated by primary or secondary rock porosity or permeability, such as karst formations or tectonic fractures.
Figure 16 Zonation of mineral deposits at the Ely, Nevada (from Theodore, 1977)
Skarn ore bodies typically exhibit irregular shapes and are relatively small in size They can appear stratabound in certain areas, reflecting the original layering of calcium-rich and calcium-poor host rocks Various metals are extracted from skarn deposits, making them significant sources for mining operations.
1 Magnetite and hematite, some pyrite and chalcopyrite, and the usual Fe-rich contact mineral such as olivine, hedenbergite, andradite and ilvaite Deposits occur in the Ural mountain (Russia), the island of Elba (Italy)
2 Cassiterite with wolfromite, scheelite, Bi, Zn and Fe minerals Deposits are known from Czecoslovakia, Namibia, Australia
3 Scheelite with sulphides of Bi, Zn, Fe, Mo, Cu, Pb well known from Canada, Nevada and USA, NE Brazil, Australia
4 Molybdenite with other sulphides of Fe, Cu, Zn and some oxides
5 Chalcopyrite with other sulphides of Fe, Zn, Mo Mines are found in the western part of the USA, in Mexico, Roumania and New Guinea
6 Sphalerite, galena with other sulphides of Fe, Cu, Zn
7 Arsenopyrite-gold and gold deposits, a rather rare type has been mined in British Columbia, Canada
8 Graphite with several small deposits and mines in the USA, Mexico, Srilanka and Grenvlle strict of Canada
Skarn deposits, such as the classic magnetite-manganese deposits in Middle Sweden and the renowned Franklin Furnace deposits in New Jersey, USA, are often not associated with igneous rocks These deposits primarily contain minerals like franklinite and willemite, which are not formed through contact metamorphism, as there are no nearby igneous rocks Instead, they result from high-grade regional metamorphism of rocks with suitable compositions, potentially of volcanogenic origin.
Igneous metamorphism Biến chất xâm nhập
Pyrometasomatism Biến chất trao đổi thay thế nhiệt
Contact metamorphism Biển chất tiếp xúc
Nongenetic term Thuật ngữ phi nguồn gốc
Lime-bearing silicate Silicat chứa vôi
Country rocks Đá vây quanh
Volatite compounds Các thành phần chất bốc
Skarn-like deposit Mỏ giống scacnơ
This chapter explores the next phase of magma consolidation, focusing on hydrothermal mineralizing solutions that can either be associated with magmas or originate from other sources These solutions may directly contribute to the formation of epigenetic mineral deposits or arise from meteoric, connate, or metamorphic waters, yet still qualify as hydrothermal solutions.