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CHAPTER 6

CHAPTER 6. CLASSIFICATION OF MINERAL DEPOSITS. Why Do We Classify Mineral Deposits?. The purpose of classifying mineral deposits is to group them into a small number of types having certain features in common. Classifications of mineral deposits

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CHAPTER 6

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    1. CHAPTER 6 CLASSIFICATION OF MINERAL DEPOSITS

    2. Why Do We Classify Mineral Deposits? The purpose of classifying mineral deposits is to group them into a small number of types having certain features in common. Classifications of mineral deposits should propose generalizations about the origin and should be applicable in field descriptions of deposits.

    3. Criteria Used in Classification of Mineral Deposits Since Middle Ages (that is since the time of Agricola), several classifications of mineral deposits have been proposed. The significant criteria used in these classifications were: morphology or form of deposit (shape, size, attitude), origin or source of ore-bearing fluid (magmatic: plutonic/volcanic, meteoric, metamorphic), metal or commodity content (Cu, Pb-Zn, Au-Ag, etc.), environment of formation or physical-chemical conditions (temperature, pressure, place of deposition: deep/shallow, host rocks, etc.), processes of deposition (open space filling, replacement, crystal settling, liquid immiscibility, evaporation, etc.)

    4. CLASSIFICATION OF MINERAL DEPOSITS Six classifications are worth mentioning. Niggli (1929) Schneiderhöhn (1941) Lindgren (1913, revised 1933, modified 1968) Bateman (1942, revised 1950, revised 1979) Stanton (1972) Guilbert and Park (1986)

    5. CLASSIFICATION OF MINERAL DEPOSITS Niggli (1929) and Schneiderhöhn (1941) classifications have historical significance. Lindgren (1913, revised 1933, modified 1968) classification is still the most important genetical classification. Bateman (1942, revised 1950, revised 1979), Stanton (1972), and Guilbert and Park (1986) classifications are easier to use in field studies.

    6. Niggli Classification Niggli considered only mineral deposits related to magmatic processes (Table 6.1). The deposits formed under high temperature-high pressure, deep-seated conditions are termed as plutonic, or intrusive; and the deposits formed under low temperature-low pressure, near-surface conditions are termed as volcanic, or extrusive. Plutonic deposits are divided into orthomagmatic, pneumatolytic to pegmatitic, and hydrothermal deposits. Here, the criterion is the nature of the ore-bearing fluid: magma, gases or fluids under high pressure, or aqueous solutions. Each group is further subdivided according to metal content and mineral associations.

    7. Table 6.1. Niggli Classification I. Plutonic, or intrusive A. Orthomagmatic 1. Diamond, platinum-chromium 2. Titanium-iron-nickel-copper a. Iron-nickel-copper sulfide/arsenide b. Titanium-iron oxide B. Pneumatolytic to pegmatitic 1. Heavy metals - alkaline earths - phophorus - titanium a. Copper-lead-zinc b. Tourmaline-rutile 2. Silicon-alkali metals-fluorine-boron-tin-molybdenum-tungsten 3. Tourmaline-quartz C. Hydrothermal 1. Iron-copper-gold-arsenic 2. Lead-zinc-silver 3. Nickel-cobalt-arsenic-silver 4. Carbonates-oxides-sulfates-fluorides II. Volcanic, or extrusive A. Tin-silver-bismuth B. Heavy metals C. Gold-silver D. Antimony-mercury E. Native copper F. Subaquatic-volcanic and biochemical deposits

    8. Schneiderhöhn Classification Schneiderhöhn also considered only mineral deposits related to magmatic processes (Table 6.2). Four main classes are recognized depending on the nature of the ore-bearing fluids: intrusive and liquid-magmatic (magma), pneumatolytic (gases under high temperature-pressure conditions), hydrothermal (aqueous solutions), and exhalation (gases and hot springs). Further subdivisions were made according to deep-seated versus near-surface conditions, mineral associations, type of deposition, host rock or gangue minerals.

    9. Table 6.2. Schneiderhöhn Classification I. Intrusive and liquid-magmatic deposits II. Pneumatolytic deposits A. Pegmatitic veins B. Pneumatolytic veins and impregnations C. Contact pneumatolytic replacements III. Hydrothermal deposits A. Gold and silver associations B. Pyrite and copper associations C. Lead-silver-zinc associations D. Silver-cobalt-nickel-bismuth-uranium associations E. Tin-silver-tungsten-bismuth associations F. Antimony-mercury-arsenic-selenium associations G. Nonsulfide associations (Iron-manganese-magnesium oxide/carbonate) H. Nonmetallic associations (Fluorite-barite-quartz) IV. Exhalation deposits

    10. Lindgren Classification Lindgren considered all types of mineral deposits, not only those related to magmatic processes (Table 6.3). Primary subdivision is into chemical and mechanical processes of concentration. Chemical processes are divided into groups according to place of deposition of minerals: in magmas, in bodies of rocks, in bodies of surface waters. Magmatic deposits are further subdivided into magmatic segregation deposits and pegmatites. Deposits formed in bodies of rocks are volcanic exhalations (sublimates, fumarolic deposits), igneous metamorphic deposits (contact metamorphic, contact metasomatic, hypothermal in carbonate rocks), hydrothermal deposits (hypothermal, mesothermal, epithermal, telethermal, xenothermal), metamorphic deposits chemical weathering deposits. Deposits formed in bodies of surface waters are termed as chemical sedimentary deposits (chemical precipitates), evaporates, volcanogenic.

    11. Table 6.3. Lindgren Classification

    12. Bateman Classification Bateman also considered all types of mineral deposits (Table 6.4). His classification is a simplified version of Lindgren's, but subdivisions are according to processes of deposition and form of deposit.

    13. Table 6.4. Bateman Classification

    14. Stanton Classification Stanton considered only metallic mineral deposits (Table 6.5). The primary subdivision is according to associated host rocks. Then, each group is subdivided using metallic associations.

    15. Table 6.5. Stanton Classification

    16. Guilbert and Park Classification Guilbert and Park considered all types of mineral deposits (Table 6.6). The primary subdivision is two-fold: according to the associated host rocks for deposits related to magmatic rocks; and according to the process of deposition for other deposits.

    17. Table 6.6. Guilbert and Park Classification

    18. CONCLUSIONS Formation of mineral deposits is a complex process, and most of the processes grade into each other by changing variables of the system such as temperature, pressure, host rock, fluid composition. Thus the classifications of mineral deposits should be flexible, and should allow gradations or intermediate classes. Niggli, Schneiderhöhn, Lindgren, and Bateman classifications are essentially similar; genesis or nature of the ore-bearing fluid is the basis of the primary subdivision in all of them. Niggli and Schneiderhöhn classifications include subdivisions for mineral-associations or metal content of the deposits. So, they may be used in the field. Lindgren tried to place physical and chemical processes in depth-temperature zones. Bateman classification is the simplest; it emphasizes the process of formation and the form of the deposit. Mineral associations may be used as modifiers.

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