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1.
An assessment of the discovered and undiscovered gold endowment of Turkey, a prolific sector in the Tethyan Metallogenic Belt, is developed from a comprehensive Geographic Information System database containing 402 gold deposits and prospects. The majority of the gold deposits and prospects are epithermal, porphyry, volcanic-associated massive sulfides, orogenic gold, and skarn systems. These five major deposit types form more than 90% of the known gold deposits and prospects. Just 87, corresponding to 21.6%, of the deposits and prospects in the data set have current calculated gold reserve and/or resources, containing a total of 54.885 Moz Au. Current gold reserves of the country are 21.447 Moz constituting 39.1% of the total gold resources, of which 17.1 Moz gold are contained in four deposits. Out of these 87 deposits and prospects, only 27 contain significant gold reserve and/or resources (defined as equal to or more than 0.32 Moz or 10 tons Au), and contain 91.8% of the total gold endowment of the country. The cumulative frequency distribution model of the gold endowment of Turkey abides by log-normal distribution. Observed and estimated 10th, 50th (median), and 90th percentiles of the data are 0.0046 Moz [0.0045 Moz estimated], 0.1030 Moz [0.0875 Moz], and 1.4969 Moz [1.6938 Moz], respectively. The 99th percentile of the data is 7.6444 Moz [18.9636 Moz]. The arithmetic mean of the known gold endowment is 0.657 Moz and the Swanson mean size is 0.492 Moz. The arithmetic mean of the 27 significant gold deposit or prospects is 1.94 Moz. Zipf’s law estimates of the undiscovered (residual) gold resources of Turkey are based on the current size of the largest, rank 1, gold deposit of Turkey, which is the Kisladag porphyry deposit that has 17.481 Moz gold endowment (including past production). Zipf’s law estimates a total of 88.261 Moz natural or total gold endowment, 57.133 Moz or 65% of which has already been found. This predicts at least 31.128 Moz residual or undiscovered gold resources to be found in Turkey, though the lack of full delineation of the rank 1 deposit, Kisladag, means that this figure is very conservative.  相似文献   

2.
The use of mineral deposit density regression models to estimate the number of undiscovered deposits is gaining acceptance in mineral resources assessments. The deposit density regression models currently in use are based on well-established power law relationships between deposit density (deposits/km2) and the areal extent of the host rocks in well explored regions (control areas) worldwide. Although these generalized or global deposit density models can generate guideline estimates that are useful at the terrane scale, locally-derived terrane-based deposit density regression models may potentially yield more relevant estimates at the terrane scale. Using 12 selected komatiite-defined control areas in the Kalgoorlie Terrane, Western Australia, we found that the size (km2) of the control areas had power law relationships with (i) nickel sulphide deposit density, and (ii) nickel endowment density (nickel metal/km2). Regression analyses showed that both power law relationships are statistically significant at the 5% level. This suggests that nickel sulphide deposit and endowment density models could be used to estimate the number of undiscovered nickel sulphide deposits and amount of nickel metal endowment in less explored komatiites in the Kalgoorlie Terrane. This study shows that global geological relationships can be viably downscaled onto local geological terranes thereby supporting the hypothesis that the processes of mineral deposit formation and preservation are scale-independent and self-similar.  相似文献   

3.
A centrographic method for analysing mineral deposit clusters is illustrated using the komatiite-hosted Kambalda nickel sulphide deposit cluster, Yilgarn craton, Western Australia. In this method, the standard distance circle divides the cluster into a more endowed inner part and a less endowed peripheral part. The standard deviational ellipse, another centrographic object, depicts the preferred northwest–southeast trend of nickel orebodies at Kambalda. Weighted centrography shows that nickel endowment is greater in the eastern than western part of the cluster. The spatio-geometric interaction of the circle and ellipse splits the cluster into several partitions. The relative concentration of nickel orebodies or endowment within a partition in relation to their concentration within the entire cluster is termed ‘capture efficiency’. Komatiite areal trace exhibits higher nickel orebody capture efficiency than spatio-geometric partitions; however, some spatio-geometric partitions exhibit nickel endowment capture efficiencies comparable to that of komatiite. Furthermore, nickel orebody and endowment capture efficiencies of komatiite are elevated only within the standard distance circle. These results suggest that at Kambalda, (i) the standard distance circle is a prime window for understanding the komatiite-hosted nickel system, and (ii) spatio-geometric partitions are plausible locales for spatial analysis of nickel orebodies and endowment. The proposed centrographic method is potentially useful in mineral resource estimations and mineral exploration targeting.  相似文献   

4.
《Ore Geology Reviews》2010,37(4):293-305
A centrographic method for analysing mineral deposit clusters is illustrated using the komatiite-hosted Kambalda nickel sulphide deposit cluster, Yilgarn craton, Western Australia. In this method, the standard distance circle divides the cluster into a more endowed inner part and a less endowed peripheral part. The standard deviational ellipse, another centrographic object, depicts the preferred northwest–southeast trend of nickel orebodies at Kambalda. Weighted centrography shows that nickel endowment is greater in the eastern than western part of the cluster. The spatio-geometric interaction of the circle and ellipse splits the cluster into several partitions. The relative concentration of nickel orebodies or endowment within a partition in relation to their concentration within the entire cluster is termed ‘capture efficiency’. Komatiite areal trace exhibits higher nickel orebody capture efficiency than spatio-geometric partitions; however, some spatio-geometric partitions exhibit nickel endowment capture efficiencies comparable to that of komatiite. Furthermore, nickel orebody and endowment capture efficiencies of komatiite are elevated only within the standard distance circle. These results suggest that at Kambalda, (i) the standard distance circle is a prime window for understanding the komatiite-hosted nickel system, and (ii) spatio-geometric partitions are plausible locales for spatial analysis of nickel orebodies and endowment. The proposed centrographic method is potentially useful in mineral resource estimations and mineral exploration targeting.  相似文献   

5.
The Iberian type of volcano-sedimentary massive sulphide deposits   总被引：6，自引：0，他引：6  
The Iberian Pyrite Belt, located in the SW Iberian Peninsula, contains many Paleozoic giant and supergiant massive sulphide deposits, including the largest individual massive sulphide bodies on Earth. Total ore reserves exceed 1500 Mt, distributed in eight supergiant deposits (>100 Mt) and a number of other smaller deposits, commonly with associated stockwork mineralizations and footwall alteration haloes. Massive sulphide bodies largely consist of pyrite, with subordinated sphalerite, galena and chalcopyrite and many other minor phases, although substantial differences occur between individual deposits, both in mineral abundance and spatial distribution. These deposits are considered to be volcanogenic, roughly similar to volcanic-hosted massive sulphides (VHMS). However, our major conclusion is that the Iberian type of massive sulphides must be considered as a VHMS sub-type transitional to SHMS. This work is an assessment of the geological, geochemical and metallogenic data available up to date, including a number of new results. The following points are stressed; (a) ore deposits are located in three main geological sectors, with the southern one containing most of the giant and supergiant orebodies, whereas the northern one has mainly small to intermediate-sized deposits; (b) ore deposits differ one from another both in textures and mineral composition; (c) Co and Bi minerals are typical, especially in stockwork zones; (d) colloidal and other primary depositional textures are common in many localities; (e) a close relation has been found between ore deposits and some characteristic sedimentary horizons, such as black shales. In contrast, relationships between massive sulphides and cherts or jaspers remains unclear; (f) footwall hydrothermal alterations show a rough zoning, the inner alteration haloes being characterized in places by a high Co/Ni ratio, as well as by mobility of Zr, Y and REE; (g) 18O and D values indicate that fluids consist of modified seawater, whereas 34S data strongly suggest the participation of bacterial-reduced sulphur, at least during some stages of the massive sulphide genesis, and (h) lead isotopes suggest a single (or homogeneized) metal source, from both the volcanic piles and the underlying Devonian rocks (PQ Group). It is concluded that, although all these features can be compatible with classical VHMS interpretations, it is necessary to sketch a different model to account for the IPB characteristics. A new proposal is presented, based on an alternative association between massive sulphide deposits and volcanism. We consider that most of the IPB massive orebodies, in particular the giant and supergiant ones, were formed during pauses in volcanic activity, when hydrothermal activity was triggered by the ascent and emplacement of late basic magmas. In these conditions, deposits formed which had magmatic activity as the heat source; however, the depositional environment was not strictly volcanogenic, and many evolutionary stages could have occurred in conditions similar to those in sediment-hosted massive sulphides (SHMS). In addition, the greater thickness of the rock pile affected by hydrothermal circulation would account for the enormous size of many of the deposits. Received: 8 September 1998 / Accepted: 4 January 1999  相似文献   

6.
The Rammelsberg polymetallic massive sulphide deposit was the basis of mining activity for nearly 1000 y before finally closing in 1988. The deposit is hosted by Middle Devonian pelitic sediments in the Rhenohercynian terrane of the Variscan Orogen. The deposit consists of two main orebodies that have been intensely deformed. Deformation obscures the original depositional relationships, but the regional setting as well as the geochemistry and mineralogy of the mineralisation display many characteristics of the SHMS (sediment-hosted massive sulphide) class of ore deposits. Rammelsberg is briefly compared to the other massive sulphide deposits in the European Variscan, including Meggen and those deposits in the Iberian Pyrite Belt. Received: 28 September 1998 / Accepted: 5 January 1999  相似文献   

7.
Mineral Deposit Densities for Estimating Mineral Resources   总被引：1，自引：0，他引：1  
Estimates of numbers of mineral deposits are fundamental to assessing undiscovered mineral resources. Just as frequencies of grades and tonnages of well-explored deposits can be used to represent the grades and tonnages of undiscovered deposits, the density of deposits (deposits/area) in well-explored control areas can serve to represent the number of deposits. Empirical evidence presented here indicates that the processes affecting the number and quantity of resources in geological settings are very general across many types of mineral deposits. For podiform chromite, porphyry copper, and volcanogenic massive sulfide deposit types, the size of tract that geologically could contain the deposits is an excellent predictor of the total number of deposits. The number of mineral deposits is also proportional to the type’s size. The total amount of mineralized rock is also proportional to size of the permissive area and the median deposit type’s size. Regressions using these variables provide a means to estimate the density of deposits and the total amount of mineralization. These powerful estimators are based on analysis of ten different types of mineral deposits (Climax Mo, Cuban Mn, Cyprus massive sulfide, Franciscan Mn, kuroko massive sulfide, low-sulfide quartz-Au vein, placer Au, podiform Cr, porphyry Cu, and W vein) from 108 permissive control tracts around the world therefore generalizing across deposit types. Despite the diverse and complex geological settings of deposit types studied here, the relationships observed indicate universal controls on the accumulation and preservation of mineral resources that operate across all scales. The strength of the relationships (R 2=0.91 for density and 0.95 for mineralized rock) argues for their broad use. Deposit densities can now be used to provide a guideline for expert judgment or used directly for estimating the number of most kinds of mineral deposits.  相似文献   

8.
The Otavi Mountain Land is a base metal sulphide ore province in northern Namibia where deposits are hosted by platform carbonates of the Otavi Group in a foreland fold-and-thrust belt on the northern edge of the Pan-African Damara Belt. Deposits have been classified as the Berg Aukas- or Tsumeb-types, based on differences in ore association, stratigraphic position and geochemistry of ores and gangue carbonates. Mineralisation at these deposits is accompanied by carbonate alteration in the form of dolomite and calcite veins, carbonate recrystallisation, calcitisation and carbonate silicification. Based on cathodoluminescence imaging, trace and rare earth element (REE), O and C isotope, and fluid inclusion data, a series of carbonate generations, constituting wall rock alteration around the Tsumeb and Kombat (Tsumeb-type) and Berg Aukas (Berg Aukas-type) deposits, was established. Similar data obtained on the recently discovered Khusib Springs deposit indicate a strong affinity to Tsumeb-type deposits. Tsumeb-type deposits are distinguished from Berg Aukas-type deposits by having trace element and REE concentrations that are significantly higher in the alteration products compared to the carbonate host rocks. Only around Tsumeb-type deposits a relative enrichment in light REE is noted for the hydrothermal carbonate generations that are cogenetic with the main stage of mineralisation. Microthermometric results from fluid inclusions in carbonate alteration phases and associated quartz indicate relatively high salinity (17–23 wt% NaCl equivalent) for the main mineralising and subsequent sulphide remobilisation stages at the deposits investigated. Estimated mineralisation temperatures are significantly higher for Tsumeb-type deposits (370–405 °C) with early sulphide remobilisation in Tsumeb at 275 °C, whereas they are lower at Berg Aukas (up to 255 °C). Fluid inclusion leachate analysis suggests that most of the observed salinity can be ascribed to dissolved, predominantly Ca- and Mg-carbonates and chlorides with subordinate NaCl. Na-Cl-Br leachate systematics indicate a derivation of the fluid salinity from the interaction with evaporitic rocks en route. Tsumeb-type mineralisation is interpreted to be derived from fluids expelled during Pan-African orogeny in the more intensely deformed internal zones of the Damara Belt further south. When the high salinity fluids reached the carbonate platform after having scavenged high concentrations of base metals, base metal sulphide precipitation occurred in zones of high porosity, provided by karst features in the carbonate sequence. Results obtained for the Berg Aukas-type deposits emphasise their derivation from basinal brines, similar to Mississippi Valley-type deposits, and confirm that mineralisation of the Berg Aukas- and Tsumeb-types are both spatially and temporally distinct. Received: 5 May 1999 / Accepted: 10 November 1999  相似文献   

9.
The use of Shortwave Infrared (SWIR) and Thermal Infrared (TIR) hyperspectral data in mineral exploration has been well documented in many mineralisation types, but is limited in komatiite-hosted nickel sulphide deposits. This project combines hyperspectral, Portable X-ray Fluorescence (pXRF) and whole-rock geochemical data to assess different analytical techniques in the exploration of these deposits. We use the Fisher East nickel sulphide prospects, Western Australia for our case study. The Fisher East prospects lie in an area of the eastern goldfields that has historically been underexplored and understudied. The rocks have undergone intense deformation with primary igneous textures being destroyed, along with strong alteration to talc carbonate assemblages. Combining different analytical tools allowed for differentiation of A and B-zones of original komatiite flows, and the reconstruction of original volcanological facies in a setting where whole rock chemistry as well as igneous textures have been substantially modified by metamorphism. By using different lithogeochemical techniques including pXRF, this study shows the Fisher East prospects are hosted within channelised komatiite flows, and have similar characteristics to Kambalda style deposits.  相似文献   

10.
The O'Toole nickel sulphide deposit is located in the Southern Plateau morphological and structural province of Minas Gerais, which has a humid tropical climate characterized by a mean temperature of 19°C and rainfall of 1600 mm. The primary ore reserve is 5.44 million tonnes at 2.72% Ni, 0.45% Cu, 0.06% Co, and 1.3 ppm combined platinum-group elements. Tropical weathering of the vertically dipping orebody has created gossans at the surface, an oxidized zone to a depth of about 20 m, and a zone of transition above fresh ore to a depth of up to 70 m. The weathering profile is similar mineralogically to the profiles at the Kambalda, Mt. Windarra, and Agnew Ni sulphide deposits in Western Australia, but differs in the depth extents of its mineralogically distinctive zones. These zones exhibit geochemically distinctive enrichments and depletions of various elements in this environment based on mass balance calculations and on the relative immobility of iridium. The work presented characterizes the geochemical behavior of Ni, Cu, Co, and platinum-group elements in the weathering of the O'Toole deposit.  相似文献   

11.
The sulphide deposits of the Iberian Pyrite Belt (IPB) represent an ore province of global importance. Our study presents 113 new sulphur isotope analyses from deposits selected to represent the textural spectrum of ores. Measured 34S values range from −26 to +10‰ mostly for massive and stockwork ores, in agreement with data previously published. In situ laser 34S analyses reveals a close correlation of 34S with texture. Primary diagenetic textures are dominated by relatively low 34S (−8‰ to −2‰), whereas stockwork feeder textures are dominated by higher 34S (∼+3‰ to +5‰). Intermediate textures (mainly coarse textures in stratiform zones) have intermediate 34S, although they are mostly dominated by the high 34S component. Rare barite has a homogeneous 34S around +18‰, which is consistent with direct derivation from Lower Carboniferous seawater sulphate. A dual source of sulphide sulphur in the IPB deposits has been considered. A hydrothermal source, derived from reduction of coeval seawater sulphate in the convective systems, is represented by sulphide in the feeder zones. Here variations in 34S are caused by variations in the extent of the sulphate reduction, which governs the SO4:H2S ratio. The second end-member was derived from the bacterial reduction of coeval seawater sulphate at or near the surface, as reflected in the primary textures. A distinct geographical variation in 34S and texture from SW (more bacteriogenic and primary textures) to NE (more hydrothermal textures and 34S) which reflects a variation in the relative input of each source was likely controlled by local geological environments. Given that the sulphur isotope characteristics of the IPB deposits are unlike most VMS and Kuroko deposits, and noting the dominance of a mixed reduced sedimentary and volcanic environment, we suggest that the IPB could represent an ore style which is intermediate between volcanic and sedimentary hosted massive sulphide types. Received: 8 October 1997 / Accepted: 14 May 1998  相似文献   

12.
 The Lengenbach Pb-Zn-As-Tl-Ba mineralisation is located in Triassic dolostones of the Penninic zone in the Swiss Alps where Alpine metamorphism reached upper greenschist to lower amphibolite grade. Geochemical data are used to constrain the origin of this unique occurrence. Two metamorphic redox environments are present: the As(III)-rich zone is controlled by barite-pyrite while the reduced zone contains graphite or pyrrhotite-pyrite and formally zerovalent As. The As(III)-rich zone is characterised by a mineral assemblage consistent with fO2 in the stability field of barite+pyrite. An As-(Pb, Tl)-rich sulphide melt coexisted with a hydrothermal fluid at >kk300 °C in this zone. Mineralised dolostones are anomalous in As, Pb, Ag, Tl, Hg, Zn, Ba, Cd, Fe, Cu, Mo, U, V, B, Ga, Cr and possibly Sn and Au (in order of decreasing enrichment). As, Pb and Zn are present in the 0.1 to 1% range, Tl and Ag reach several hundred ppm. Uraninite is concentrated in silicate-rich bands and yields a late Alpine U-Pb age of 18.5±0.5 Ma. Pb- and S isotopic variations are interpreted by metamorphic overprinting and re-equilibration within an isochemically metamorphosed mineralisation. Hydrothermal sulphides are more strongly affected by uranogenic Pb than massive Pb-As-sulphides representing a former sulphide melt. The least overprinted mineralisation is characterised by 206Pb/204Pb U003U=18.44−18.56, 207Pb/204Pb=15.60−15.75, 208Pb/204Pb =38.44−38.84 and δ34S (sulphide)=−25±2‰. S isotopic variations are largely a result of sulphide-sulphate re-equilibration yielding temperatures of 450± 30 °C. 87Sr/86Sr ratios of mineralised samples are lower than or equal to host dolostones, precluding major infiltration of basement-derived fluids during Alpine metamorphism. The Sr source (87Sr/86Sr close to 0.708) probably was seawater with a radiogenic, detrital mineral component. The genesis of the unique Lengenbach mineralisation is interpreted as the result of isochemical metamorphic overprinting of a carbonate hosted stratiform sulphide mineralisation. Well-crystallised sulphide minerals in fissures and druses formed during retrograde cooling of a sulphide melt in equilibrium with a hydrothermal fluid. The primary mineralisation was probably formed at or close below the sea floor and fed by sulphide-poor hydrothermal fluids. Sulphide was largely derived from seawater by open system bacterial sulphate reduction. U, V and Mo may be seawater-derived. Received: 1 February 1995/Accepted: 10 January 1996  相似文献   

13.
The Silesia–Cracow district in Poland has been one of the world’s principal sources of zinc from nonsulfide zinc ore (Polish: galman). The still remaining nonsulfide ore resources can be estimated at 57 Mt at 5.6% Zn and 1.4% Pb. Nonsulfide mineralization is mainly hosted by Lower Muschelkalk (Triassic) limestone and is associated with different generations of the hydrothermal ore-bearing dolomite (OBD I, II, III). A fundamental ore control is believed to have been exerted by the basement faults, which were repeatedly reactivated during the Alpine tectonic cycle, leading to the formation of horst-and-graben structures: these dislocations may have caused short periods of emersion and the circulation of meteoric waters during the Cenozoic. Nonsulfide ores show a wide range of morphological characteristics and textures. They occur as earthy masses, crystalline aggregates, and concretions in cavities. Breccia and replacement textures are also very common. The most important mineral phases are: smithsonite, Fe–smithsonite, Zn–dolomite, goethite, and Fe–Mn(hydr)oxides. Minor hemimorphite and hydrozincite have also been detected. Two distinct nonsulfide ore types occur: the predominant red galman and the rare white galman. In the white galman, Fe–smithsonite and Zn–dolomite are particularly abundant. This ore type is commonly considered as a peripheral hydrothermal alteration product related to the same fluids that precipitated both the OBD II–III and the sulfides. In contrast, a supergene origin is commonly assumed for the red galman. Evidence of the petrographic and mineralogical difference between white and red galman is also found in stable isotope data. Smithsonite from red galman shows a limited range of δ 13CVPDB values (−10.1 to −11.4‰), and δ 18OVSMOW values (25.3‰ to 28.5‰, mean 26.8 ± 0.3‰). The uniform and low carbon isotope values of red galman smithsonite are unusual for supergene carbonate-hosted deposits and indicate the predominance of a single organic carbon source. Smithsonite from white galman has a more variable, slightly more positive carbon isotope (−2.9‰ to −7.4‰), but broadly similar oxygen isotope composition (26.8‰ to 28.9‰). The relationship of the white galman ore with the hydrothermal system responsible for OBD II and sulfide generation is still uncertain. The most important paleoweathering events took place in both Lower and Upper Silesia during Late Cretaceous up to Paleogene and early Neogene time. During this period, several short-lasting emersions and intense weathering episodes facilitated the formation of sinkholes in the Triassic carbonate rocks and the oxidation of sulfide orebodies through percolating meteoric waters. These phenomena may have lasted until the Middle Miocene.  相似文献   

14.
Measurable molybdenum isotope fractionation in molybdenites from different ore deposits through time provides insights into ore genesis and a new technique to identify open-system behavior of Re–Os in molybdenites. Molybdenite samples from six porphyry copper deposits, one epithermal polymetallic vein deposit, four skarns, and three Fe-oxide Cu–Au deposits were analyzed. The δ97Mo‰ (where ) for all samples varied from 1.34 ± 0.09‰ to −0.26 ± 0.04‰. This is the largest molybdenum isotopic variation in molybdenite from high-temperature ore deposits recorded to date. δ97Mo‰ of molybdenite varies as a function of the deposit type and the rhenium and osmium concentrations of the samples. Isotope values for Mo also vary within the individual deposits. In general, molybdenites from porphyry copper deposits have the lightest values averaging 0.07 ± 0.23‰ (1σ). Molybdenites from the other deposit types average 0.49 ± 0.26‰ (1σ). The variations could be related to the fractionation of Mo into different mineral phases during the ore-forming processes. A comparison of the Mo isotope ratios and the Re–Os ages obtained from the same aliquot may possess a geochronological evaluation tool. Samples that yielded robust ages have different Mo isotopic compositions in comparison to samples that yielded geologically unreasonable ages. Another observed relationship between the Re–Os and Mo isotope data reveals a weak correspondence between Re concentration and Mo isotope composition. Molybdenites with higher concentrations of Re correspond to lighter Mo isotope values.  相似文献   

15.
Summary Kristiansenite occurs as a late hydrothermal mineral in vugs in an amazonite pegmatite at Heftetjern, T?rdal, Telemark, Norway. Tapering crystals, rarely up to 2 mm long, are colourless, white, or slightly yellowish. The mineral has the ideal composition Ca2ScSn(Si2O7)(Si2O6OH) and is triclinic C1 with cell parameters a = 10.028(1), b = 8.408(1), c = 13.339(2) ?, α = 90.01(1), β = 109.10(1), γ = 90.00(1)°, V = 1062.7(3) ?3 (Z = 4). It has a monoclinic cell within ∼ 0.1 ? and is polysynthetically twinned on {010} by metric merohedry. The strongest reflections in the X-ray powder pattern are [d in ?, (I obs), (hkl)]: 5.18 (53) (1–11), 3.146 (100) (004), 3.089 (63) (−222), 2.901 (19) (221), 2.595 (34) (222), 2.142 (17) (−3–31). The Mohs’ hardness is 5?–6; Dcalc. = 3.64 g/cm3; only a mean refractive index of 1.74 could be measured. Scandium enrichment in the Heftetjern pegmatite and the crystal chemistry of scandium are briefly discussed. Received April 30, 2001; accepted July 28, 2001  相似文献   

16.
A newly discovered, extensive sphalerite-bearing breccia (~7.5 wt.% Zn) is hosted in dolomitised Carboniferous limestones overlying Ordovician–Silurian metasedimentary rocks on the Isle of Man. Although base metal sulphide deposits have been mined historically on the island, they are nearly all quartz vein deposits in the metamorphic basement. This study investigates the origin of the unusual sphalerite breccia and its relationship to basement-hosted deposits, through a combination of petrographic, cathodoluminescence, fluid inclusion, stable isotope and hydrogeologic modelling techniques. Breccia mineralisation comprises four stages, marked by episodes of structural deformation and abrupt changes in fluid temperature and chemistry. In stage I, high-temperature (T h > 300°C), high-salinity (20–45 wt.% equiv. NaCl) fluid of likely basement origin deposited a discontinuous quartz vein. This vein was subsequently dismembered during a major brecciation event. Stages II–IV are dominated by open-space filling sphalerite, quartz and dolomite, respectively. Fluid inclusions in these minerals record temperatures of ~105–180°C and salinities of ~15–20 wt.% equiv. NaCl. The δ34S values of sphalerite (6.5–6.9‰ Vienna-Canyon Diablo troilite) are nearly identical to those of ore sulphides from mines in the Lower Palaeozoic metamorphic rocks. The δ18O values for quartz and dolomite indicate two main fluid sources in the breccia’s hydrothermal system, local Carboniferous-hosted brines (~0.5–6.0‰ Vienna standard mean ocean water) and basement-involved fluids (~5.5–11.5‰). Ore sulphide deposition in the breccia is compatible with the introduction and cooling of a hot, basement-derived fluid that interacted with local sedimentary brines.  相似文献   

17.
The Elshitsa volcanic hosted massive sulphide deposit occurs in the central part of the Srena Gora metallogenic zone in Bulgaria. The gold-bearing massive sulphide mineralization is considered to be the product of an island arc volcano-plutonic process and hydrothermal activity that took place during the Late Cretaceous. In addition to the major gold-hosted opaque minerals such as pyrite, chalcopyrite, sphalerite and galena there are minor phases of tennantite, goldfieldite, Se-bearing aikinite, native silver and bornite in the massive sulphide lenses and stringer zones. Most of the sulphide minerals are Se-bearing. All of the six mineral assemblages that were deposited during the pyrite and copper-pyrite stages of mineralization are gold-bearing. The gold tenor as a rule is less than 1 g/t. Native gold and electrum occur as blebs or intergranular particles in the sulphide minerals. Gold in the early massive pyrite is of submicroscopic type (< 0,1 μm) and of colloidal ori-gin. Pyrite deformation and recrystallization in the temperature range 250°–160 °C has led to Au and Ag migration to cracks and grain boundaries of the sulphide minerals. As a result of these process the native gold and electrum grain size increases from submicroscopic (< 0,1 μm) in the early colloform pyrite to microscopic (0,1–100 μm) and macroscopic (> 100 μm) in the late gold-sulphide assemblages. The electrum fineness in 41 individually studied grains varies between 780 and 992‰ with a mean of 895‰. Native silver was found in association with bornite. Cu, Te, Sb and Bi are the most common trace-elements in gold and electrum. The Cu-Zn-Pb association is most important as a Au-Ag-carrier. A model for gold behaviour during sulphide deformation is proposed involving coarsening of gold grain size from the earlier to the later sulphide mineral assemblages. Received: 4 December 1995 / Accepted: 23 September 1996  相似文献   

18.
The Marcona–Mina Justa deposit cluster, hosted by Lower Paleozoic metaclastic rocks and Middle Jurassic shallow marine andesites, incorporates the most important known magnetite mineralization in the Andes at Marcona (1.9 Gt at 55.4% Fe and 0.12% Cu) and one of the few major iron oxide–copper–gold (IOCG) deposits with economic Cu grades (346.6 Mt at 0.71% Cu, 3.8 g/t Ag and 0.03 g/t Au) at Mina Justa. The Middle Jurassic Marcona deposit is centred in Ica Department, Perú, and the Lower Cretaceous Mina Justa Cu (Ag, Au) prospect is located 3–4 km to the northeast. New fluid inclusion studies, including laser ablation time-of-flight inductively coupled plasma mass spectrometry (LA-TOF-ICPMS) analysis, integrated with sulphur, oxygen, hydrogen and carbon isotope analyses of minerals with well-defined paragenetic relationships, clarify the nature and origin of the hydrothermal fluid responsible for these contiguous but genetically contrasted deposits. At Marcona, early, sulphide-free stage M-III magnetite–biotite–calcic amphibole assemblages are inferred to have crystallized from a 700–800°C Fe oxide melt with a δ18O value from +5.2‰ to +7.7‰. Stage M-IV magnetite–phlogopite–calcic amphibole–sulphide assemblages were subsequently precipitated from 430–600°C aqueous fluids with dominantly magmatic isotopic compositions (δ34S = +0.8‰ to +5.9‰; δ18O = +9.6‰ to +12.2‰; δD = −73‰ to −43‰; and δ13C = −3.3‰). Stages M-III and M-IV account for over 95% of the magnetite mineralization at Marcona. Subsequent non-economic, lower temperature sulphide–calcite–amphibole assemblages (stage M-V) were deposited from fluids with similar δ34S (+1.8‰ to +5.0‰), δ18O (+10.1‰ to +12.5‰) and δ13C (−3.4‰), but higher δD values (average −8‰). Several groups of lower (<200°C, with a mode at 120°C) and higher temperature (>200°C) fluids can be recognized in the main polymetallic (Cu, Zn, Pb) sulphide stage M-V and may record the involvement of modified seawater. At Mina Justa, early magnetite–pyrite assemblages precipitated from a magmatic fluid (δ34S = +0.8‰ to +3.9‰; δ18O = +9.5‰ to +11.5‰) at 540–600°C, whereas ensuing chalcopyrite–bornite–digenite–chalcocite–hematite–calcite mineralization was the product of non-magmatic, probably evaporite-sourced, brines with δ34S ≥ +29‰, δ18O = 0.1‰ and δ13C = −8.3‰. Two groups of fluids were involved in the Cu mineralization stage: (1) Ca-rich, low-temperature (approx. 140°C) and high-salinity, plausibly a basinal brine and (2) Na (–K)-dominant with a low-temperature (approx. 140°C) and low-salinity probably meteoric water. LA-TOF-ICPMS analyses show that fluids at the magnetite–pyrite stage were Cu-barren, but that those associated with external fluids in later stages were enriched in Cu and Zn, suggesting such fluids could have been critical for the economic Cu mineralization in Andean IOCG deposits.  相似文献   

19.
Toumaline is widespread in the host strata of strata-bound base metal sulphide deposits in the Devonian metallogenic district around Shanyang-Zhashui in eastern Qinling. As a member of the schorl-dravite series, the tourmaline is characterized by Mg > Fe and Na > Ca, showing apparent chemical zonation which records the geochemistry during its formation and subsequent regional metamorphism and hydrothermal overprint. The close similarity in chemical and isotopic constitutions between the tourmaline of the main metallogenic epoch in this district [FeO/(FeO + MgO)=0.34 − 0.39 and δ11B=−7.6‰ − − 8.8‰] and those related to massive sulphide deposits typical of submarine (exhalative) hydrothermal sedimentation may add further support to a similar mechanism of mineralization for the strata-bound deposits in the district. Supported by the Foundation for Young Scientists under the National Natural Science Foundation of China.  相似文献   

20.
《Ore Geology Reviews》2007,30(3-4):177-241
Australia's nickel sulfide industry has had a fluctuating history since the discovery in 1966 of massive sulfides at Kambalda in the Eastern Goldfields of Western Australia. Periods of buoyant nickel prices and high demand, speculative exploration, and frenetic investment (the ‘nickel boom’ years) have been interspersed by protracted periods of relatively depressed metal prices, exploration inactivity, and low discovery rates. Despite this unpredictable evolution, the industry has had a significant impact on the world nickel scene with Australia having a global resource of nickel metal from sulfide ores of ∼ 12.9 Mt, five world-class deposits (> 1 Mt contained Ni), and a production status of number three after Russia and Canada. More than 90% of the nation's known global resources of nickel metal from sulfide sources were discovered during the relative short period of 1966 to 1973. Australia's nickel sulfide deposits are associated with ultramafic and/or mafic igneous rocks in three major geotectonic settings: (1) Archean komatiites emplaced in rift zones of granite–greenstone belts; (2) Precambrian tholeiitic mafic–ultramafic intrusions emplaced in rift zones of Archean cratons and Proterozoic orogens; and (3) hydrothermal-remobilized deposits of various ages and settings. The komatiitic association is economically by far the most important, accounting for more than 95% of the nation's identified nickel sulfide resources. The ages of Australian komatiitic- and tholeiitic-hosted deposits generally correlate with three major global-scale nickel-metallogenic events at ∼ 3000 Ma, ∼ 2700 Ma, and ∼ 1900 Ma. These events are interpreted to correspond to periods of juvenile crustal growth and the development of large volumes of primitive komatiitic and tholeiitic magmas caused by large-scale mantle overturn and mantle plume activities. There is considerable potential for the further discovery of komatiite-hosted deposits in Archean granite–greenstone terranes including both large, and smaller high-grade (5 to 9% Ni) deposits, that may be enriched in PGEs (2 to 5 g/t), especially where the host ultramafic sequences are poorly exposed.Analysis of the major komatiite provinces of the world reveals that fertile komatiitic sequences are generally of late Archean (∼ 2700 Ma) or Paleoproterozoic (∼ 1900 Ma) age, have dominantly Al-undepleted (Al2O3/TiO2 = 15 to 25) chemical affinities, and often occur with sulfur-bearing country rocks in dynamic high-magma-flux environments, such as compound sheet flows with internal pathways facies (Kambalda-type) or dunitic compound sheet flow facies (Mt Keith-type). Most Precambrian provinces in Australia, particularly the Proterozoic orogenic belts, contain an abundance of sulfur-saturated tholeiitic mafic ± ultramafic intrusions that have not been fully investigated for their potential to host basal Ni–Cu sulfides (Voisey's Bay-type mineralization). The major exploration challenges for finding these deposits are to determine the pre-deformational geometries and younging directions of the intrusions, and to locate structural depressions in the basal contacts and feeder conduits under cover. Stratabound PGE–Ni–Cu ± Cr deposits hosted by large Archean–Proterozoic layered mafic–ultramafic intrusions (Munni Munni, Panton) of tholeiitic affinity have comparable global nickel resources to many komatiite deposits, but low-grades (< 0.2% Ni). There are also hydrothermal nickel sulfide deposits, including the unusual Avebury deposit in western Tasmania, and some potential for ‘Noril'sk-type’ Ni–Cu–PGE deposits associated with major flood basaltic provinces in western and northern Australia.  相似文献   

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