Sulfide Bodies Research Articles

Basaltic glass with high-temperature equilibrated immiscible sulphide bodies with native iron from disko, central West Greenland

Immiscible sulphide bodies show eutectic quench textures in a basaltic glass rock (mg=66) from a native iron-bearing dyke chilled at T=1,200° C and P=250 bars. The sulphide bodies are composed of troilite (90–91%), iron (9–10%) and very scarce vanadium-rich chromite and approach a ternary cotectic in the Ni-poor part of the system Fe-Ni-S. Transition element partition between olivine (mg=83), silicate glass (mg=59) and sulphide blebs indicate that the phases were equilibrated at 1,200° C. D vanadium(olivine/glass) is close to unity and reflect the reducing nature of the rock, for which estimates of f O2∼10−12 to −13 and f S2∼10−5 have been made. D nickel, cobalt, copper (sulphide/glass)=4,300, 230 and 380 respectively, are much higher than reported experimentally determined D's onmonosulphide/basalt glass at the same temperature and show increasing positive deviation (ΔNi>ΔCo>ΔCu) with the increasingly siderophile character of the elements. K Dnickel-iron (sulphide/olivine)=63 is much higher than an experimentally reported value (33) and comparison with published thermodynamic data on Ni-partition between olivine and iron metal suggests that the positive deviation is roughly proportional to the excess metal component in the sulphide melt. The occurrence of strongly Ni-depleted reduced basalts on Disko shows that fractionation of metal and sulphides was a common and geologically important process.

Effect of graphite on the enhancement of surficial geochemical anomalies originating from the oxidation of sulphides

Abstract Geochemical studies carried out on the Melville Peninsula, N.W.T. have found strongly anomalous Zn and Ni contents in lake sediments and surface waters draining sphalerite and pentlandite mineralization in graphitic paragneiss. The area is within the zone of continuous permafrost of the Canadian Shield. The levels found are greater than are present near non-graphitic massive sulphide mineralization in similar climatic and topographic settings elsewhere in the northern Shield. Oxidation of sulphides is an electrochemical process. A sulphide body acts as a conductor immersed in an electrolyte (the groundwater). In permafrost terrain the electrolyte is unfrozen water present as interfacial films in the permafrost and also the water of the summer-thawed, “active layer”. Electrons flow through the body from oxidizing, anodic sites to upper, cathodic zones, where they take part in the reduction of O2 dissolved in groundwater. The circuit is completed by ion flow within the electrolyte. As the upper portion of sulphide body is replaced by non-conducting oxidation products, access of O2 to the cathodic zones is reduced and the rate of oxidation decreases. However, for bodies that contain significant graphite, electron flow is maintained through the oxidized layer to near-surface, oxygen-rich horizons. Thus the rate of oxidation of graphitic base metal sulphides is likely to be greater than for partially oxidized non-graphitic bodies. The rate of oxidation is a factor in determining the flux of mobile base metals carried away from mineralization in solution, and hence the levels of anomalies present in drainage sediments and waters. Whereas this work has been directed to a permafrost regime, similar principles apply to other environments where graphite connects oxidizing sulphides to levels with higher partial pressures of O2, up to the water table. Other conductors, such as sulphide minerals relatively resistant to oxidation, may act in a similar fashion to graphite.

MPPO-1, Crone PEM, SP, Ground Magnetic, MIP and Turam Data Over Drilled Massive Sulphide Mineralisation at Steeple Hill, W.A.

When results of MPPO-1, Crone PEM, SP, MIP, and Turam surveys are compared over a drilled massive sulphide body, the consistency of the results is not necessarily as absolute as the geophysical profession may wish.

Metallogenesis along a fossil oceanic fracture zone: Arakapas fault belt, Troodos Massif, Cyprus

The Arakapas fault belt, southern Troodos Massif, which is interpreted as a fossil oceanic fracture zone, contains a sedimentary and volcanic “fill” including basaltic lava breccias, volcaniclastic sandstones, intercalated Fe-rich mudstones, and minor Cu sulphide mineralisation. The volcaniclastic sedimentary rocks were produced by submarine weathering and gravity redeposition of basalt within the transform zone. In contrast, the Fe-mudstones predominantly originated as chemical precipitates from hydrothermal solutions generated by hydrothermal leaching of basalt by seawater. The rare earth elements, and some trace metals, including Co, Ni, Pb, V and Zr, are thought to have been incorporated from seawater into the ferruginous precipitates. Unusually high Fe/Mn ratios of the Fe-mudstones relative to most modern ocean-ridge sediments may reflect deposition in relatively oxygen-depleted waters on the floor of a major bathymetric depression created by the transform faulting; release of acidic thermal waters would have further suppressed Mn precipitation. Contrary to recent suggestions of metallogenesis along oceanic fracture zones, none of the major Cyprus cupriferous sulphide bodies lie along the fossil Arakapas transform zone.

The feasibility of delineating non-layered anomalous velocity zones by a combination of fan shooting and least-squares analysis

Laboratory velocity measurements on nickel-sulphide samples show that the velocity contrast between a sulphide body and rocks typical of the Canadian Shield can be fairly large. In view of this, the feasibility of delineating the sulphide body by means of a combination of fan shooting and least-squares analysis was examined by both computer model simulation and field experimentation. The method consists, essentially, of shooting several fans emanating from the perimeter of a rectangle around the suspected location of a deposit, and measuring the corresponding first arrival times. The rectangle is then divided into grid units, and the apparent velocity in each grid unit is found by least-squares solutions of an overdetermined system of linear equations.The computer model tests indicate that in cases where the velocity contrast between the surrounding medium and the anomalous zone is good, and each medium homogeneous, the method is a potentially useful auxiliary technique for mining exploration. However, field tests show that these requirements (i.e., good velocity contrast and homogeneity of each medium) may constitute a serious limitation of the method.

Geology of the massive sulfide deposits of Campo Morado, Guerrero, Mexico

The Campo Morado group of massive sulfide deposits is situated in the northern part of the State of Guerrero, Mexico. The oxide portions of a number of these deposits had been mined prior to 1939, principally for gold and silver. Between 1973 and 1977, a program of exploration at Reforma, the largest known deposit of the Campo Morado group, delineated several million metric tons of massive pyritic sulfides grading at 3.12 pecent Zn, 1.07 percent Pb, 0.68 percent Cu, 111.8 grams per metric ton Ag, and 1.2 grams per metric ton Au.The Campo Morado bodies belong to a class of mineral deposits characterized as strata-bound, polymetallic, massive sulfides, believed by many to be genetically related to felsic volcanic rocks and to have formed as a result of a process which might be termed exhalative-sedimentary.The Campo Morado massive sulfide deposits are generally lenticular and they are peneconcordant within a shallow-water volcano-sedimentary sequence of Lower Cretaceous age. All of the known deposits are associated with laharic breccias. The sulfide bodies consist of pyrite, sphalerite, chalocpyrite, galena, tetrahedrite, arsenopyrite, marcasite, and pyrrhotite in decreasing order of abundance. The pyrite contains gold and silver and the tetrahedrite carries silver. Compositional zoning is present within the sulfide bodies. The sulfide grains are very fine and they are intergrown. The major gangue mineral with the sulfides is quartz in both cryptocrystalline and crystalline forms.It is suggested in this paper that the Campo Morado group of massive sulfide bodies was deposited in an environment transitional between a true volcanogenic and a true sedimentary environment.

Experiments to demonstrate mobility of metals in waters near base-metal sulphides

During the oxidation of a base-metal sulphide body, Cu, Pb and Fe are immobilised to varying degrees in sulphide residues and surrounding soils. However, Zn is relatively mobile and is a useful pathfinder element in groundwaters.Using material from the Woodlawn orebody, experiments were performed which simulated reactions in the intermediate subsurface ore zone where oxygen and carbon dioxide are Absent, and downward percolating waters contain metals leached in surface zones. Two simulation series were performed; one represented moderate percolation rates (0.7 cm/s) and the other slow percolation (0.04 cm/s).Results suggest that waters enriched in Cu, Pb and Zn from surface weathering of sulphides, seeping at the slow rate through a sulphide deposit out of contact with the atmosphere would lose these metals completely. If the waters were seeping at the moderate rate, only Cu would be completely lost, levels of Pb and Fe would be greatly reduced and Zn levels virtually unchanged. Metals in solution were exchanged with metals in the sulphide in the order Cu2+ > Pb2+ > Fe2+ > Zn2+. Possible explanations regarding some aspects of gossan morphology and supergene enrichment are afforded by the experimental data.

Geochemical dispersion patterns associated with the Lake Yindarlgooda sulphide mineralization, Western Australia

Geochemical investigations have been carried out in the Lake Yindarlgooda area, 40 km east of Kalgoorlie, Western Australia, where sulphide deposits and black shales occur in a sequence of metavolcanics and metasediments of the Eastern Goldfields greenstone belt. The studies were made in order to understand the processes of element migration and the formation of dispersion patterns in semi-arid regions having partly lateritic weathering conditions. Outcrop exposure in the vicinity of the mineralized zones is limited to the siliceous caprock and gossans. Mineralogical data, and geochemical data on the distribution of Cu, Ni, Co, Zn, Pb and other elements, have been obtained from unweathered and weathered rocks, and different horizons of the overlying soil in the area surrounding the mineralized zones of Lake Yindarlgooda, Scotia and Ringlock. The results indicate, in principle, two different kinds of weathering environment: (1) playa lakes, with the development of solonchaks; and (2) Tertiary peneplains outside the playa lakes, with lateritic soils, solonized brown soils or desert loams. The trace element distribution patterns in the solonchaks are determined only by the initial element content of the alluvial sediments. Therefore, sampling of solonchaks generally cannot be recommended for geochemical exploration surveys, but sampling of weathered bedrock below the solonchaks is highly recommended in the playa lake environment. By sampling of the bedrock, the non-outcropping continuation of the Lake Yindarlgooda sulphide body has been precisely delineated. In areas of the Tertiary peneplains outside the playa lakes, lateritic soils, solonized brown soils or desert loams cover the weathered bedrock. Comparative geochemical investigations in these areas in the vicinity of the nickel sulphide deposits at Scotia and Ringlock have shown that the migration of elements in solution is restricted, a result of the very low water table. In this area the main process of dispersion is mechanical. Therefore, the secondary dispersion haloes of Scotia and Ringlock are narrow, restricted to a few tens of metres, and sampling at closer intervals is needed to locate the orebodies.

Rare earth elements as hydrothermal tracers during the formation of massive sulfide deposits in volcanic rocks

Massive, tabular sulfide bodies commonly occur within sequences of subaqueous volcanic rocks. They are believed to form as chemical sediments when hydrothermal solutions which derived metals from interaction with the volcanic rocks flow out into sea water. Such a water-rock interaction, hydrothermal exhalation model implies that changes in the composition of the hydrothermal solutions result from changing conditions within the hydrothermal system and that the different metal contents of the resulting chemical sediments are related to different alteration reactions. It is suggested that the rare earth elements (REE), because of their coherent and somewhat predictable geochemical properties, can serve as tracers of the alteration reactions which take place within these hydrothermal systems. Changes in the reactions should be reflected by the REE pattern of the solution which will in turn influence the REE pattern of the resulting deposit.In order to test this hypothesis the REE patterns of massive sulfide deposits and associated rocks from the Bathurst-Newcastle District, New Brunswick, Canada, were determined by instrumental neutron activation analysis (INAA). Interpretation of the REE data was aided by a simple computer model which predicted solution REE patterns resulting from various solution-rock interactions.Chlorite-rich samples have REE distributions and abundances that are very similar to those of shales which suggests a detrital source for their REE. Other chemical sediment samples, except Cu-rich sulfides, have positive europium anomalies. The magnitude of the Eu anomaly and the amount of heavy REE enrichment increase with increasing content of oxide and sulfide minerals. Samples with high contents of Pb sulfides have the highest Eu anomalies and the strongest enrichments of heavy REE and these characteristics do not correlate with the abundance of any other mineral.The observed patterns are best explained by an input of hydrothermal solutions to the site of chemical sedimentation. Because of the characteristic REE patterns and consistent stratigraphic positions of the chemical sediment zones (Cu-rich sulfides, Pb + Zn-rich sulfides, and iron-formation) the following sequence of events apparently took place within the hydrothermal system: 1. Alteration of ferromagnesian minerals and/or volcanic glass released Cu and Fe to the solution (Cu-sulfide zone). 2. Preferential alteration of feldspar by a very concentrated brine enriched the solution in Pb, Zn, Ba, and heavy REE (Pb + Zn-sulfide zone). 3. Continued removal of Fe from the volcanic rocks without alteration of a large amount of the solid phases (iron-formation). Results of the REE study are consistent with the formation of massive sulfide deposits by precipitation from solutions which derived metals from volcanic rocks during water-rock interactions. In fact, the data require that water-rock interactions take place and are incompatible with direct release of magmatic water onto the sea floor. Generation of solutions capable of precipitating Pb-rich massive sulfide deposits requires that phenocrysts of feldspar are present in the volcanic rocks, that the rocks are felsic and that conditions within the hydrothermal system favor alteration of feldspar. A relation should then exist between the metal contents of sulfide deposits and the composition of the host volcanic pile. As expected, deposits in mafic lavas are Cu rich while those in mixed, mafic-felsic piles have Pb + Zn/Cu ratios which increase with the felsic rock content of the volcanic pile.

Metal distribution at Stekenjokk: Primary and metamorphic patterns

Abstract The metal distribution in the metamorphosed, stratiform, Fe-Zn-Cu sulphide deposit (Kieslager) of Stekenjokk is studied. Obvious thickening and thinning of the ore body took place during an early isoclinal fold phase. Reconstruction of the pretectonic morphology indicates an elongated and thickened sulphide body. Primary zoning indicates way-up in the volcano-sedimentary sequence. Metamorphic mobilization and redeposition are selective and of certain importance for the ore geometry. Control of combined distribution patterns is necessary for the economic exploitation of the deposit.

Geological setting of the Skorovas orebody within the allochthonous volcanic stratigraphy of the Gjersvik Nappe, central Norway

Synopsis The Skorovas orebody is one of the chief stratiform basemetal deposits within the allochthonous greenstone belt of the Central Norwegian Caledonides. It is contained in the volcanic level of a complex eruptive association of Lower to Middle Ordovician age defined as the Gjersvik Nappe. The rocks of this nappe are contained as a depressed segment of the larger Köli Nappe and defined to the north and south, respectively, by the Börgefjell and Grong-Olden basement culminations. The principal components of this nappe are a plutonic infrastructure of composite gabbroic intrusions within which has been emplaced a series of dioritic to granodioritic (trondhjemitic) bodies that form the roots of a consanguineous submarine polygenic volcanic sequence. The eruptive rocks are overlain unconformably by a sequence of polymict conglomerates and calcareous flysch sediments, the composition of which suggests immediate derivation by erosion from the underlying igneous complex. Pre-tectonic segregations, veins and vesicle fillings of epidote, albite, chlorite, carbonate and quartz related to primary volcanic flow structures in the lava pile provide evidence of pervasive in-situ sea-floor metamorphism, and this interpretation is verified by the abundance of nearly monomineralic epidote clasts in the derived conglomerates. The relationship of the eruptive and sedimentary suites is interpreted in terms of the evolution of an ensimatic island arc, of Lower to Middle Ordovician age, which underwent uplift and erosion prior to emplacement on the Fennoscandian basement during the climactic stages of collision tectonism of the Caledonian Orogeny in Silurian times. The entire igneous and sedimentary assemblage has been affected by the tectonic stages of allochthonous emplacement, but the gross differences in competence between the component lithologies has resulted in a particularly heterogeneous style of deformation in which folding, componental sliding, fracturing and penetrative metamorphic refabrication have been governed largely by the geometry of the most competent lithologies, notably gabbro, diorite and granodiorite (trondhjemite) intrusives and, within the extrusive sequence, compact dacitic flows and their spilitized aphanitic equivalents (keratophyres). The heterogeneous pattern of deformation is resolved in terms of two main stages of folding complicated by componental sliding movements. Mineralization occurs at two levels in the eruptive sequence. The layered gabbros and lensoid metagabbros of the plutonic infrastructure contain small cumulus bodies of nickel-, copper- and platinum-bearing pyrrhotite-pyrite-magnetite ore of magmatic derivation. Mineralization of this type is at present only known in sub-economic quantities. The Skorovas orebody, in common with other widely dispersed volcanic exhalites in the Gjersvik Nappe, occurs within the volcanic sequence at a level marked by episodes of explosive dacitic volcanism and associated fumarolic activity. The Skorovas orebody consists of approximately 10 000 000 tons of massive and disseminated predominantly pyritic ore with an approximate average grade of 1.3% Zn and 1.0% Cu, together with trace amounts of Pb, As and Ag. The complex lensoid geometry of the orebody is resolved in terms of the disjunction of a single stratiform unit by tight isoclinal folding and componental movements, probably involving both translation and rotation. Enrichment of sphalerite, chalcopyrite and, locally, galena within the magnetite-pyrite ores at the stratigraphic top and margins of the ore lenses is interpreted as a primary feature. The banded magnetite-pyrite ores are commonly associated with magnetitic cherts or jaspers and are thus transitional in aspect to the thin, iron- and silica-rich, basemetal-depleted, exhalative sedimentary horizons that occur extensively within the extrusive sequence of the Gjersvik Nappe. These are interpreted as the products of settling of colloidal iron and silica hydrosols following explosive dispersal into an oxidizing submarine environment. They are valuable time-stratigraphic markers and indicators of way-up in complicated structures and are a potentially valuable tool in exploration for massive sulphide bodies formed in limited reducing environments.

Geochemical dispersion in mineralized soils of a permafrost environment

Abstract The Agricola Lake massive sulphide body occurs in metavolcanic rocks of Archean age in the northwestern Canadian Shield. The mineralization contains Zn, Cu, Pb, Ag and Au and, in addition, there are elevated contents of As and Hg. The area lies within the zone of continuous permafrost. The distribution of elements in soils in the vicinity of the mineralization shows the influence of three independent dispersion processes — glacial, solifluction and hydromorphic — superimposed on the primary bedrock distribution. Oxidation of sulphides has been active in the past and continues to this day. In the absence of large amounts of carbonate minerals, this has produced an acidic weathering environment. The most mobile of the elements studied — Zn — has been largely removed from the mineralized soils and dispersed a considerable distance down drainage. Au, Hg, Pb and Ag are relatively immobile and are retained in the soils overlying mineralization or in nearby, glacially dispersed detritus. Fe, Cu and As are of intermediate mobility and are deposited in the proximal portion of the drainage system. The estimated order of mobility is: Zn > Cu > Fe > As > Ag > Pb > Hg > Au. Glacial action dispersed oxidized detritus, already depleted in mobile elements. Material precipitated along the proximal portion of the drainage system shows an association of As and Cu with iron oxides and Ag and Hg with manganese oxides. In addition to the elements discussed above, Mg in soils indicates the alteration zone underlying the massive sulphide and Ca outlines the soils subject to acidic leaching.

Experimental aqueous dispersion of elements around sulfides

The dispersion of elements in rocks around sulfide deposits has been simulated in laboratory tanks at normal temperatures and pressures as part of an investigation to determine the causes of anomalous geochemical patterns in rocks associated with volcanic-sedimentary sulfide deposits. The same broad characteristics found in field examples--Zn generally concentrated in the footwall, Pb concentrated in the hanging wall, and a relative deficiency of Na and Cu around the sulfide\---|also developed in the laboratory simulations. While the mechanisms of dispersion are not well understood, they are probably influenced by electrochemical control of sulfide dissolution, the pH and Eh of the electrolyte, and electrical potential gradients around the sulfide body. A generalized electrochemical model is proposed as the possible fundamental controlling mechanism.

An Application of Downhole Electrodes in IP Exploration

A 45 m overburden layer having a conductivity 10 times that of the underlying host rock covers a sulphide body under study. It is estimated that this overburden will attenuate surface IP signal potentials to below 1/25 of that produced if the overburden is replaced by host material. By placing the pair of current electrodes down existing boreholes (75 m apart) at a depth of 1.6 times the thickness of the overburden this attenuation is completely overcome. Type curves showing diagnostic features are presented for traverses with potential electrodes remaining on the surface.

The geology of Prieska Copper Mines Limited

The discovery of the Prieska Copper Mines Ltd. copper-zinc orebody in South Africa in 1968 focused the attention of economic geologists on the little-known Bushmanland gneiss area to the west of the Kaaien quartzites, where intensive exploration recently has resulted in at least two additional major discoveries.The main Prieska orebody, with a probable age of 1,250 m.y., and the Volgelstruisbult Annex massive sulfide body occur in a series of quartz-feldspar rocks, quartz-biotite gneisses, and quartz-plagioclase-amphibole gneisses which are interpreted as metamorphosed volcanic rocks of calc-alkaline affinity, called the Copperton Volcanic Pile, which have been infolded into the basement complex.A major crustal fracture, the Copperton fault, bounds the Copperton Volcanic Pile and an assemblage of more basic volcanic rocks, the Van Wyks Pan Volcanic Pile, in the east and plays a role in the preservation of the Kaaien quartzites.Metamorphism of upper amphibolite rank has destroyed many of the volcanic textures in the Copperton Volcanic Pile but the preservation of lithic and crystal pyroclastic fragments, amygdales, flow banding, and shards is nevertheless spectacular. Inclusions are also common in the massive sulfide bodies.Wall-rock alteration of the phyllic and propylitic type is present around both the sulfide bodies but is not well understood.The main Prieska orebody comprises four main textural types--porphyroblastic, granular, hackly, and disseminated, and there is a tendency for zinc to occur preferentially with the granular type.Mineralogical zoning occurs over the areal extent of the orebody but not through the width of the massive sulfides, and there is a tendency for zinc to occupy the lateral edges of the orebody while copper is relatively evenly spread.Textural and stratigraphic evidence suggests that the main Prieska orebody represents a pre-existing sulfide mass, possibly a stockwork ore, which was redeposited by volcanic action.

FINITE‐ELEMENT COMPUTATION OF SEISMIC ANOMALIES FOR BODIES OF ARBITRARY SHAPE

A method which uses observed frequency spectral ratios of seismic plane waves for exploration of ore bodies is now available. The new method is based on the numerical solution of the response of a two‐dimensional shallow structural anomaly to an upward‐moving seismic wave from a distant earthquake or explosion. Finite‐element analysis is used for both P- and S-waves. Solutions to the direct problem for bodies of arbitrary shape have not previously been available. Results in the time and frequency domains are discussed here for a salt ridge and for a massive sulfide body. For the inverse problem, interpretation using contours of spectral ratios along a surface profile is suggested.

Multispectral aerial photography as exploration tool IV–V: An application in the Khomas trough region, South West Africa; and cost effectiveness analysis and conclusions

This paper is the fourth and last in a series devoted to the evaluation of “text-book” multispectral aerial photography (TMSAP) as exploration tool. The first part of the paper describes a survey that attempted to identify gossaniferous outcrops which are the surface expression of certain massive sulphide bodies. Conventional colour (Kodak 2448) and false colour infrared (Kodak 2443) photography was acquired for comparative purposes. It was found that of these photographic techniques, the multispectral gave the best discrimination between the gossaniferous outcrop and the background rock types. The second part of the paper presents our overall conclusions regarding the effectiveness of TMSAP in exploration applications. It is noted that although TMSAP enhances spectral differences between object categories, these differences can generally also be detected on conventional photography. Out of the total of 55 pairwise discriminations between object categories that were sought in the course of our 4 experiments, TMSAP performed significantly better than conventional photography in only 7 cases. This slight superiority of TMSAP is outweighed by important theoretical, practical and economic limitations. It is demonstrated that the cost of a TMSAP survey can be typically an order of magnitude greater than the cost of a conventional photographic survey. These factors preclude TMSAP as an effective exploration tool.

Role of Fluid State Mobilization during Metamorphism of the Henderson Ore Bodies, Chibougamau, Quebec, Canada

The Henderson Cu-Au deposit occurs in discordant structures within the anorthosite zone of the Doré Lake Complex. The Doré Lake Complex is intruded into volcanic rocks of the Chibougamau greenstone belt on the southeastern side of the Superior Province. Massive to disseminated sulfide ores are associated with sericite, carbonate, chlorite and/or chloritoid schists within a large 'shear zone'. These ores show structural and textural evidence of intense deformation, recrystallization, and metamorphic mobilization.The deposit comprises not only sulfide schist ore with alternating sulfide and schist layers, but also 'hydrothermal' vein-type segregation ore. The latter is characterized by sulfide-bearing quartz-calcite veins that occur in the 'shear zone' and in the subsidiary fractures adjacent to it.The sulfide schist and vein types of ores can be attributed to partly solid state mobilization combined with fluid state mobilization from a pre-existing ore, and is an excellent example of extensive fluid state mobilization of sulfides under relatively low-grade regional metamorphism. It is suggested that fluid state mobilization can play an important role during the metamorphism of a pre-existing sulfide body, especially in the presence of differential stress accompanied with rupture. The deformational features of the ore are the important indication for syn- and/or pre-metamorphic origin of the ore.

The mercury in sulfide deposits emplaced in volcanic suites

Massive sulfide deposits in the Pacific and Ural provinces have varying mercury contents. The latter is lower in metamorphosed ores than in unmetamorphosed or in young ones. Two varieties of cenozoic sulfide ores are distinguished: 1) products of subcontinental solfataric action with high mercury content in pyrites, accompanied by cinnabar, 2) products of postvolcanic activity in submarine suites with low mercury content in sulfides (Kurokotype). A distribution of mercury between coexisting sulfides (in descending rank) corresponds to the sequence: sphalerite-chalcopyrite-pyrite. During metamorphism, sulfides loose their mercury (pyrite in higher degree than chalcopyrite). It is possible that mercury vaporised from sulfides has some influence on the formation of mercury ores at some distance from metamorphosed sulfide bodies within the same region.

An integrated geo-electrical survey on the nangaroo copper—zinc prospect, near Leonora, Western Australia

High-grade massive copper—zinc sulphides were intersected during exploration diamond drilling of a prospect in the Nangaroo area, Western Australia. Further diamond drilling had little success and a programme of down-hole and surface exploration geophysical techniques was applied in an attempt to obtain information on the geometry and extent of the sulphides etc. This programme consisted of applied potential/IP potential surveys utilising a current electrode placed directly within the massive sulphide drill intersection, electrical logging of available drill holes and a surface gradient array I.P. survey. The applied potential/IP potential data were successful in providing potential patterns at the surface indicating the strike extension and up plunge direction of the sulphide body. The combination of applied potential/IP potential data, drill hole electrical logs and gradient array IP data provided complementary information on the mineralis ation and this permitted estimation of the dip and plunge of the body and indicated the presence of two discontinuities. The combined data indicated a shallow mineralised body with a gentle northerly plunge and a steep dip to the west. Subsequent diamond drilling confirmed the extent and attitude of the body indicated by the geo-electrical data. Later research studies confirmed the electrical properties of the mineralisation and showed that the mineralisation was a moderate EM conductor.