Supergene gold enrichment in the castromilserra da quinta. Verwoerd 1957 recognised that vanadium deposition occurred substantially later than sulphide emplacement. The main nickel and copper supergene enrichment zone is located near the central axis of target 19 positioned roughly over two peridotite layers defined by the recent aircore and diamond drilling. Download limit exceeded you have exceeded your daily download allowance.
Supergene gold mobility in orogenic gold deposits, otago schist, new zealand 5 ore, and a substantially greater proportion of that nearsurface gold was free particles fig. Metavolcanic host rocks, mineralization, and gossans of. Geological background the lavrion area is part of the attic cycladic crystalline belt, which is a. However, the activities of microorganisms in secondary copper deposition sillitoe et al. The supergene enrichment is the only process known to record these events. Occasionally, some of the leachedout soluble metals can reprecipitate below the water table developing zones of secondary sulphide enrichment chavez, 2000, williams, 1990. Metavolcanic host rocks, mineralization, and gossans of the. Definitions definition from evans leaching of valuable elements from the upper parts of mineral deposits and their precipitation at depth to produce higher concentrations definition from guilbert and park supergene enrichment occurs when oxidizing acids dissolve metal ions from the protore and redeposited it in more. You can see the oxidation zone, consisting of the gossan, the leached zone and the oxidised zone. A very highgrade in situ to exotic limoniteclay cuoxidemineral zone is locally developed above impermeable dolomite at the base of chalcociteclay zone. Tharsis, rio tinto, were also mined during roman times for precious metals velasco et al. Evidence for the supergene origin of alunite in sediment. The fact that wellauthenticatedsupergene parageneses have.
Initial products of supergene oxidation, copiapo mining. The paleoclimatic signatures of supergene metal deposits. Supergene oxidized and enriched porphyry copper and related. Controls on supergene enrichment of porphyry copper deposits. Mineral deposition was controlled mainly by ph conditions, p co2, metal ion activities e. Controls on supergene enrichment of porphyry copper. The earliest mineral workings in the ipb gossans back as far as ca. Definition secondary or supergene enrichment where leaching of materials occurs and precipitation at depth produces higher concentrations. Supergene oxidized and enriched porphyry copper and. First, the enrichment may be primarily the result of the chemical removal of a large part of the gangue minerals, in which case the gold migrates slowly downward by gravity or is left behind as a residual.
As host for the largest and richest porphyry copper deposits. Ore deposits outside the r2 occur along lineaments and result often from supergene enrichment. Below the water table is a zone of supergene enrichment in which secondary sulfide minerals such as covellite and chalcocite form from chalcopyrite and copper sulfate in. The supergene enrichment of gold in deposits may take place by a simple mechanical process, by chemical means, or by a combination of these. Supergene enriched, intrusion related low suphidation. Since the rio tinto deposits are in many ways analogous with the norwegian massive sulphide deposits, it would seem logical to expect that a supergene enrichment zone, in the case of the latter, would also contain much chalcocite. The geologic history of oxidation and supergene enrichment in. Supergene enrichment occurs when oxidizing acids dissolve metal ions from the protore and re deposits it in more reducing, basic areas, i. Residual mineral deposits an existing mineral deposit can be turned in to a more highly concentrated mineral deposit by weathering in a. Supergene enrichment of the khanong copper resource, sepon. The characterization of the hydrothermal and supergene alterations was based on detailed mapping, extensive use of the pima short wave infrared spectrometer, petrography, xrd and microprobe. Sulphide minerals are unstable to highly unstable in surface conditions, as witnessed by the collection curators headache known as pyritedecay, which can turn a freshly collected shiny pyritized ammonite into a pile of stinking, sulphurous fragments within weeks in the worst cases. Oxidation supergene enrichment linkedin slideshare. Concentrating minerals by chemical weathering processes.
Definition of supergene enrichment a mineral deposition process in which nearsurface oxidation produces acidic solutions that leach metals, carry them downward, and reprecipitate them, thus enriching sulfide minerals already present. Metals that have been leached from the oxidized ore are carried downward by percolating groundwater, and react with hypogene sulfides at the supergene hypogene boundary. Domingos massive sulphide orebodies is described and correlated with the supergene kaolinitehalloysite alteration observed. Superposition of the advanced oxidation of colloform pyrite, an enrichment in impurities sphalerite, galena, and tennantite from the primary ores, stagnant water conditions, an elevation of the water table during oxidation, and bacterial activity led to supergene concentrations of the base metals as sulphide, selenides or sulphosalts. The ore thus enriched forms the secondary, or supergene sulfide, zone and overlies the primary, or. In situ supergene enrichment of the sulphide protore has resulted in a highgrade chalcociteclay zone 10. Oxidation and secondary enrichment of gold deposits. At the ashanti concession, ghana, goldbearing quartz veins and disseminated sulphide lodes occur in narrow m shear zones with altered argillites and metatholeiite host rocks.
Geology and origin of supergene ore at the lavrion pbag. Harraz presentation supergene enrichment 2 outline of topic 9. Multiphase origin of the cuco ore deposits in the western. The formation of secondary concentrations of ni co significant enough for an economic resource requires a protolith lithology that is primarily enriched in ni. Supergene enrichment how natural processes have transformed.
The khanong supergeneenriched copper resource, 23 mt at 3. Metal cations and sulfate anions are released through oxidative weathering of sulfide minerals in the aerated or vadosezone. Supergene gold mobility in orogenic gold deposits, otago schist, new zealand. Many sulphide ores are oxidised in this process and brought into solution. The contrasting sites in this study represent a progression in the development of supergene conditions that occur in relatively high energy fluvial settings. Formation of supergene minerals took place under near. Geology and origin of supergene ore at the lavrion pb. The ore thus enriched forms the secondary, or supergene sulfide, zone and overlies the primary, or hypogene, zone. Supergene enrichment how natural processes have transformed lowgrade copper mineralization into economic ores by david f. Published models that have strongly influenced exploration policy suggest that supergene enrichment ceased at 14 ma due to an increase in aridity. The process acts on elements with multiple oxidation states in a controlled complex manner related to ev, ph, and ionic matrix. Copper sulfide enrichment in supergene deposits has largely been considered an abiotic process brimhall, et al.
Sulfide oxidation and leaching of ore deposits in the weathering environment, and any attendant secondary sulfide enrichment, are supergene processes ransome, 1912, implying that they are products of descending aqueous solutions of surface derivation. Alunite veins versus supergene kaolinitehalloysite. At the contact of oxidised and sulphide ores lies a supergene zone of enrichment which has provided a contrast, not formerly imagined, to eluras primary development and stoping operations. Although these environments might be distin guished by their geologic characteristics, alunite in sedimenthosted micron gold deposits has been. Important gossans developed from primary volcanogenic massive sulfide vms deposits are preserved and described in the iberian pyrite belt ipb, and some of them e. The supergene enrichment blanket is overlain by an intensely altered and leached fe oxiderich gossan the remains of the original massive sulfide that extends upward to the paleosurface. Detailed descriptions of supergene mineralization in the ipb are scarce. Mature oxidation and enrichment are promoted by the following. The porphyry copper deposits of southwestern north america were developed in a continental margin cratonic setting, above a subduction zone that was active largely from the early mesozoic to. Definition weathering processes and supergene ore deposits conditions. The development and evolution of supergene gold and sulphide.
Such complexes may be present where the oxidation potential is high in oxidizing sulphide zones and where h,so, and an. Supergene enrichment occurs at the base of the oxidized portion of an ore deposit. Introduction ore deposits are crustal concentrations of useful elements that can be exploited at a pro. The reaction produces secondary sulfides with metal contents higher than those of the primary.
The enriched ore forms the supergene zone above the primary or hypogene zone. Supergene alteration of norwegian sulphide deposits a query. It forms during the supergene sulphide ore enrichment, when weakly acid surface water perloctaes through the mineral deposit. Because of the soft nature of the ore, intense ground support practice has been combined with a panel cut and fill continuous mining system to extract a.
Supergene alunite also termed secondary supergene by hayba et al. The development and evolution of supergene gold and. Supergene processes include the predominance of meteoric water circulation with concomitant oxidation and chemical weathering. The enriched ore forms the supergene zone above the primary or hypogene zone and in some cases can hold as much as ten times the original metal. These results suggest a supergene enrichment in upper zones of the deposit. Supergene sulfide enrichment, in geology, natural upgrading of buried sulfide deposits by the secondary or subsequent deposition of metals that are dissolved as sulfates in waters percolating through the oxidized mineral zone near the surface.
Gossan or the iron cap supergene sulphide ore enrichment. The macraes mine is the only modern mine in otago, and is therefore the only deposit to provide a window into the deeper parts of a mineralised system below the. In ore deposit geology, supergene processes or enrichment are those that occur relatively near the surface as opposed to deep hypogene processes. Supergene features and evolution of gossans capping massive.
However, the oftencomplex mineralogy of supergene ores poses serious challenges to extractive metallurgy or mineral processing, and many supergene enrichment blankets will remain unmined or unprocessed until such time as viable metallurgical processes can be developed. The stratiform mineralization form the largest group and can be found mainly in lower roan r2 rocks, which can be identi. These include giant supergene enriched deposits such as those at morenci in arizona 4. Supergene sulphide enrichment is the natural upgrading of buried sulphide deposits by the secondary deposition of metals dissolved in waters percolating through the rock generally from surface down. Below the water table is a zone of supergene enrichment in which secondary sulfide minerals such as covellite and chalcocite form from chalcopyrite and copper sulfate in solution. Q for geologists about supergene enrichment supertopo. Supergene sulfide enrichment, also called secondary enrichment, in geology, natural upgrading of buried sulfide deposits by the secondary or subsequent deposition of metals that are dissolved as sulfates in waters percolating through the oxidized mineral zone near the surface. In this particular case, the variable oxidation state element is copper. Report on the ore mineralogy of samples from the lagoa. The descending meteoric waters oxidize the primary sulfide ore minerals and redistribute the metallic ore elements. The geologic history of oxidation and supergene enrichment. Aircore drilling doubles nickel and copper supergene. Mcqueen crc leme, australian national university, canberra, act 0200 and school of rehs, university of canberra, act 2601. The development and evolution of supergene gold and sulphide mineralisation that occurs in quartz pebble conglomerates qpcs from two contrasting environments is investigated.
In this work, we present the implication of the discovery. In ore deposit geology, hypogene processes occur deep below the earths surface, and tend to form deposits of primary minerals, as opposed to supergene processes that occur at or near the surface, and tend to form secondary minerals. Supergene features and evolution of gossans capping. The economic viability of these deposits is dependent on the size and quality of their supergene enrichment blanket.
Gold 111 salts of oxyanions are not very stable, but complex auric sulphates of the type auso, are known. Supergene sulphides and related minerals in the supergene. Supergene enrichment is essential for the economic viability of many porphyry copper deposits reich and vasconcelos 2015 this issue, and determining when and how supergene enrichment has occurred is important when exploring for enriched and exotic copper deposits mote et al. At great depth the pressure is high, and water can remain liquid at temperatures well above 100 c. The age of the supergene ore is poorly constrained, but presumably pliocene. The mineralisation is concealed by up to 10 m of kaolinitemica forest ochrosol soils, beneath which is a saprolitic zone of leached rock extending down 6070 m to the hypogene ore zone. The unusual style of hypogene mineralisation and unique set of conditions have resulted in the development and preservation of a supergeneenriched profile in. Nico laterites are supergene deposits of ni co formed from the pervasive chemical and mechanical weathering of ultramafic rocks. Supergene px0308 supergene px0309 supergene px0310 supergene px0311 157. In the iberian pyrite belt ipb, most of the volcanogenic massive sulphide deposits and related stockworks are capped by a more or less well developed and preserved gossan. Supergene enriched, intrusion related low suphidation deposit, binebasebawone, north sulawesi, indonesia doi. In the more than 50 years which have elapsed since the recognition and characterization of the phenomena of supergene oxidation and enrichment, this economically significant topic has received remarkably little attention. Jul 09, 2015 the main nickel and copper supergene enrichment zone is located near the central axis of target 19 positioned roughly over two peridotite layers defined by the recent aircore and diamond drilling.
Significance of supergene enrichment supergene sulphide enrichment is the natural upgrading of buried sulphide deposits by the secondary deposition of metals dissolved in waters percolating through the rock generally from surface down. This is so because it denotes a concretion of iron hydroxides that has formed on top of sulphide mineral vein, where it reaches the surface. However, harvesting microorganisms from the supergene zone and using them. The central andes host some of the worlds largest porphyry copper deposits.
1157 1459 1455 827 1297 1414 808 1497 314 1408 961 734 277 289 873 473 1248 683 1023 1636 338 1253 1542 52 110 48 497 1296 691 1416 213 1078 987 936