Relationship exists between mineral systems/ore deposits, principal commodities and critical minerals. Very good illustration have been made in clear cut pictures explaining the various tectonic domain wherein what type of deposits are formed. By repeated explanations with world / Indian examples have to be given to the Geologists community by showing the models where one can look for the expected ore mineral deposits and what type of tectonic set up is favorable for their formation.
I have been requested to offer my Opinion on a recent report by the US Geological Survey suggesting a new method of classification of “mineral system” based deposit classification FOR EARTH MAPPING RESOURCES.
Yes, This new classification would provide better clarity of the complex science of mineral exploration and equip them with better understanding to be a more successful explorer.
Yes, the emphasis has to be given while teaching the students in line with System-Deposits-Commodities-Critical mineral table Open File Report 2020-1-42 for the Earth Mapping resources Initiative”.
The table has clearly indicated the relationship existing between mineral systems/ore deposits, principal commodities and critical minerals and the very good illustration have been made in clear cut pictures explaining the various tectonic domain wherein what type of deposits are formed. By repeated explanations with world / Indian examples have to be given to the Geologists community by showing the models where one can look for the expected ore mineral deposits and what type of tectonic set up is favorable for their formation.
Though they have given priority of Phases I (REE), II (Al, C, Co, Li, Nb, PGE, Sn, Ta, Ti and W), and III ( to locate As, BaSO4, Be, Bi, CaF2, Cr, Cs, Ga, Ge, He, Hf, In, KCl, Mg, Mn, Re, Rb, Sb, Sc, Sr, Te, U, V and Zr) for exploring the different set up of minerals, it can be taken up as a necessity based at this juncture.
Both Table-I and different schematic models are quite exhaustive, I suggest some of the following points for your kind observation.
Prior to the initiation of the above said view, that the budding geologists have to be given an valuable exposure to the geochemistry wherein the great affinity of certain elements with other elements have to be explained. So when we are looking for certain ore bearing minerals, one has to bear in mind that a mineral has the affinity for certain other minerals which commonly occur together in good quantity or in negligible amount. Sometimes those associated minerals may act the role of indicators to locate the minerals what we look for. Eg: Geochemical indicators for gold include: silver, copper, lead, zinc, cobalt, nickel, arsenic, antimony, tellurium, selenium and mercury. Similarly the compositions of PGM and micro inclusions in them, and the dominant associated mineral assemblages of silicates, oxides, sulphides and type of texture, morphology composition and alteration testify to several possible primary source indicators of PGE mineralization., Similarly for locating diamond-presence of omphacite pyroxene and pyrope garnet are path finders).
Hence it is very essential to deal with the various forms of mineral compound viz.,– sulphides, oxides, carbonates, tellurides, etc., and the nature of formation has to be known in detail which will help in effectively narrow down the search area for many different types of ore deposits in mineral exploration.
Moreover, I draw your kind attention to the following:
The publication of Indian Bureau of mines FNO: 215(1)/UNFC/ME(I)2003 dt.3.6.2003 deals with the guidelines under MCDR for UNFC of mineral reserves/resources (see rule 4591)© and form H-1 to H-8 and H-9), it is understood that the field guidelines which are simply formatted to adopt the UNFC are in seven categories; ie all mineral/ ore formations or deposits fall under these seven categories which may deal with specific mineral assemblages exclusive to this deposit nature: they are
- Stratiform, strata bound, tabular deposit of regular habits : Principal kinds of minerals involved are coal seams, lignite beds, iron ore formations, manganese horizons, bauxite cappings, chromite in ultramafics, dolomite, limestone, baryts, gypsum, evaporites ( including postash and salt beds), chalk, fineclay and fullers, earth;
- Stratiform, strata bound, tabular deposit of irregular habits: Principal kinds of minerals involved.. in addition to the above said minerals, gold in banded iron formation, platinum group of elements in chromite bearing rocks and molybdenum in shear- controlled zones.
- Lenticular bodies of dimensions including bodies occurring in enechelon, Silicified linear zones composite veins: Principal kinds of minerals in this category are: Base metal sulphides, supergene iron and manganese bodies in lateritised bodies, bauxite-cobalt and nickel lateroids, auriferous quartz reefs, PGM in association with sulphides, graphite lenses, porphyry deposit of copper, molybdenum, tin, pyrite and pyrrhotite bodies.
- Lenses, veins and pockets; stock works, irregular shaped, modest to small size bodies: Multimetal sulphide bodies of Cu, Pb, Zn, Sb, Hg, Cr, Sn-Ag, tektite bodies, skarn bodies of sheelite, powellite, wollastonite, fluorite etc., semiprecious minerals, veins of apatite, barite and asbestos veins, magnesite lenses, vermiculite, magnesite lenses, mica in pegmatite, pyrophyllite lenses and veins, high grade bauxite , clay pockets, ochre and bentonite clays and diamond pipes.
- Gem stones and rare metal pegmatites, reefs and veins: Tin-tungston-tantalum-molybdenum veins and pegmatite, beryl, topaz, emerald, cesium deposits, mineralization associated alkaline rocks, veins and plugs of carbonatite.
- Placer and residual mineral deposits of Hills and valley wash: Placer tin and gold deposits, monazite, garnet, ilmenite, rutile, diamonds in conglomerate, floats of corundum, kyanite, sillimanite and magnetite etc.,
- Dimension stones: Colored varieties including granite, syenite, schists, gneisses, marbles, slate, sandstones, migmatites etc., black varieties of diorite, dolerite, gabbro etc, sills/ batholiths of anorthosite / gabbro etc.,
in which the principal associated minerals/ores are grouped and systematically prospected from Reconnaissance, Prospecting to General and further Detail stages of exploration like G4, G3, G2 and G1 categories by assigning the quantum of different surveys like aerial reconnaissance, geological, geochemical, geophysical, technological studies (including pitting , trenching, sampling, drilling, core sampling- chemical analysis), petrographic study, minerographic study, geostatistical analysis, to delineate exact nature of the deposit reserve/ resource.
In such cases, while assigning the programme, the fixation of the target and execution of methodology have been formulated. This special knowledge has to be brought to the knowledge of the students/ professionals which help them to understand the clear cut objective of the projects and the methodology adopted to achieve the cent percent results on any assigned programme.
Moreover in the year 2011, in the Secretariat of Mission Head II, GSI, Nagpur where the undersigned worked, had implemented the practice and while the Geologists writing their technical report, they are advised to follow this UNFC classification wherein they will aware in which type of deposits and what stage of exploration of work they do and what exactly expected further for improvement and achievement of the objective.
This methodology without any iota of doubt, helps to bring out all the world resources without any lacunae in the scientific advancement of works to elevate the mineral deposit from G4 to G1 category with all economic feasibility and viability of exploration.
An attempt has been made to prepare an abstract of the Table-I of Hofstra and Kreiner (2020)
TABLE-I SHOWS THE ABSTRACT OF SYSTEMS-DEPOSITS-COMMODITIES-CRITICAL MINERALS TABLE FOR THE EARTH MAPPING RESOURCES INITIATIVE:
| No | System name | Geological environment /set up | MAIN CRITICAL MINERALS ASSOCIATED |
| 1 | PLACER (RIVERINE,MARINE, RESIDUAL,ELUVIAL,ALLUVIAL, SHORLINE, PALAEO) | DRAINAGE BASINS, SHORLINE,TIDAL AND WIND DRIVEN | AU, PGE, U,Sn ,W, FLUORITE,REE, Nb, Ta,Ti Mn ETC., |
| 2 | CHEMICAL WEATHERING | STABLE AREAS OF LOW TO MODERATE RELIEF BY CHEMICAL LEACHING—BAUXITE, Ni-LATERITE-CARBONATE LATERITE | Ni, Al, Co, REE, Ga, U,PGE, Mn |
| 3 | METEORITIC RECHARGE | OXIDISED DESCENDING WATER SCAVENGES | U,V,Sr,REE,Re |
| 4 | LACUSTRINE EVAPORITE | CLOSED DRAINAGE BASINS WATER FROM METEORITE,SURFACE, GROUND, GEOTHERMAL RECHARGE WATER EVAPORATE AND PRODUCES | SALT,GYPSUM,POTASH BORATE, NITRATE, Li ETC., |
| 5 | MARINE EVAPORITE | SEA WATER EVAPORATE | SALT, GYPSUM, POTASH ETC., |
| 6 | BASIN BRINE PATH | MARINE EVAPORITES CONNECTED WITH LOWERGROUND AND LATERAL PERMEABLE STRATA—ORE FLUIDS SCAVENGING METALS | Cu, Pb,Zn,POTASH, Li,Hg,U,V, Ba,REE,Co, Sr,PGE, Ge,Ga, |
| 7 | Marine chemocline rim | LOCATION WHEREIN BASIN BRINES DISCHARGE INTO OCEAN—CHEMICAL DESIMENTATION | PHOSPHATE,V,Ni,PGE, REE,Co |
| 8 | HYBRID MAGMATIC REE/ BASIN BRINE PATH | HYBRID SYSTEM WITH CO2 AND HF BEARING MAGMATIC VOLATILES– REPLACE CARBONATES WITH FLUORITE | FLUORITE, REE, Ti, Nb,Ba,Be ETC., |
| 9 | ARSENIDE | CONTINENTAL RIFT SYSTEMS-DEEP SEATED- ASCENDING OXIDISED-METAL RICH BRINES-PRECIPITATION OF NATIVE ELEMENTS | AG,As,Co,Bi,Ni,U,Sb |
| 10 | VOLCANOGENIC SEA FLOOR | VOLCANOGENEIC SEA FLOOR MAGMATIC ARC, BACK ARC BASIN | Cu,Zn POLY METALLIC SULPHIDES, Ba, Mn ETC. |
| 11 | OROGENIC | FLUID FLOW DURING EXHUMATION OF VOLCANIC SULPHIDES, CARBONACEOUS, CALCAREOUS SILICATES | Au,Ag,MERCURY, GRAPHITE, Sb, W |
| 12 | COEUR –DE- ALENE TYPE | DEWATERING OF OXIDISED SEQUENCES DURING EXHUMATION / METASEDIMENTARY HOST ROCKS/ | POLYMETALLIC SULPHIDES& ANITMONY (Cu,Pb Zn,Sb,Co,Ge, Ga |
| 13 | METAMORPHIC | RECRYSTALLISED ORGANIC CARBON/REE AND PHOSPHATE MINERALS | GRAPHITE, REE, U,TH,Y |
| 14 | PORPHYRY Cu-Mo-Au | POLYMATALLIC SULPHIDES, GREISSEN, SKARN DEPOSITS | Mo,W,Sn,PGE, Te,Sb,As |
| 15 | ALKALIC PORPHYRY | OCEANIC, CONTINENTAL MAGMATIC ARC,CONTINENTAL RIFT ZONES FLUIDS EXSOLVED FROM FRACTIONATED ALKALIC PLUTON | Mo,Bi,W, PGE,Au, Ag,Cu,V,F ETC., |
| 16 | PORPHYRY Sn (GRANITE RELATED) | GRANITE RELATED S-TYPE PORPHYRY TYPE PERALUMIOUS PLUTONS | ENRICHED IN W,Au,Ag,Cu,Pb,Zn ETC.,, |
| 17 | REDUCED INTRUSION RELATED | CONTINENTAL MAGMATIC ARCS—FLUIDS EXSOLVED FROM CALC ALKALINE PLUTONS | ENRICHED IN W,Au,Ag,Te,Bi, AND As |
| 18 | CARLIN TYPE | CONTINENTAL MAGMATIC ARCS | Au,Ag,Sb,As |
| 19 | CLIMAX TYPE | CONTINENTAL RIFTS WITH HYDROUS BIMODAL MAGMATISM | Nb,Ta,Be Mo, W,Au, ,Te,Bi, AND As, FLUORITE,,U,Sn |
| 20 | IOA-IOCG | SUBDUCTION AND RIFT RELATED PROVINCE | U,REE, Co,Re, Mn,Bi,Te |
| 21 | MAGMATIC REE | CONTINENTAL RIFT SYSTEM OR ALONG TRANSLITHOSPERIC STRUCTURE.REE IN MANTLE DERIVED ULTRTABASIC, ALKALINE, PERALKALINE INTRUSIONS | CARBONATE, P, REE, Zr, Hf,Nb,Y,Ba, Zr, MAGNETITE,VERMICULITE |
| 22 | MAFIC MAGMATIC | LARGE IGNEOUS PROVINCES RELATED TO MANTLE/ METEORITE AND LAYERED INTRUSIONS | Cr, Co, PGE, Ni, Cu, Ag, Au, Ti, V, REE |
The above, twenty type of systems falling under different environments of geological set up and the same thing was explained in different models by Hofstra and Kreiner (2020) it is quite exhaustive and clearly understandable.
The MCDR 7 stage of classification is a simplified form for the execution of exploration work in systematic manner to achieve the target.
Hence it is an efficient approach globally to streamline the USGS earth mapping resources initiative to achieve the objective in a short span of time and no other type of deposits are left and the UNFC procedure may be adopted while exploring the mineral deposits.
Mineral Exploration Academy 