Molybdenite Mineralization Research Articles

The Endako Batholith: Episodic Plutonism Culminating inFormation of the Endako Porphyry Molybdenite Deposit, North-Central BritishColumbia

The Endako batholith is a composite batholith that consists of early foliated hornblende ± biotite diorites, intermediate-age unfoliated hornblende ± biotite diorites, and late granodiorites to monzogranites. These latter plutons host the Endako molybdenite deposit, a major porphyry deposit located in the central Canadian Cordillera. Extensive K-Ar dating on the batholith had given relatively reproducible ages centered on 140 Ma, indicating a short life span for magmatic activity. However, a combined U-Pb and 40Ar/39Ar study has resulted in a substantial reappraisal of the age and time span of intrusive activity and its association with molybdenite mineralization. The new data show that the batholith had a protracted emplacement history, covering ~75 m.y., with clear evidence for periods of magmatic quiescence. The oldest magmatic suite of the Endako batholith, the Stern Creek suite, is dated at ~220 Ma and comprises foliated gabbros and diorites. Mafic to intermediate plutons of the Stag Lake suite range in age from 180 Ma to 161 Ma. The Francois Lake suite is divided into two subsuites: the Glenannan subsuite dated at 157 Ma to ~155 Ma and the 149 to 145 Ma Endako subsuite that hosts the Endako molybdenite deposit. 40Ar/39Ar dating of hydrothermal biotite indicates molybdenite mineralization is genetically associated with terminal stages of magmatic activity. Biotite within the mine had its 40Ar/39Ar systematics reset at ~145 Ma by hydrothermal fluids with temperatures in excess of 300°C. This resetting is associated with intrusion of the 145.1 ± 0.2 Ma Casey phase monzogranite, the youngest phase within the Endako subsuite. A further partial resetting of biotite is interpreted to be coeval with Eocene intrusion of the high-level, miarolitic Sam Ross Creek phase and numerous mafic dikes that cut through the region. Hydrothermal fluids associated with this latter event were below biotite closure temperature and do not appear to have any relationship to molybdenite mineralization within the Endako deposit. The new geochronologic data, coupled with detailed mapping, show a general age progression from mafic plutonism at the margins to a central core of high-level granodiorite to monzogranite. The data document the existence of a long-lived, relatively stationary magmatic center. Pulsed magmatism, evident even within individual magmatic suites, may play a major role in concentrating and ultimately depositing molybdenite in some porphyry systems. At Endako, molybdenite would have formed within the higher level portions of the batholith, a position that would normally have rendered the deposit prone to erosional removal. However, subsequent Eocene extensional block faulting may explain the preservation of this Jurassic deposit, which is the oldest economic molybdenite deposit in the Cordillera of North America.

Two ages of porphyry intrusion resolved for the super-giant Chuquicamata copper deposit of northern Chile by ELA-ICP-MS and SHRIMP

Zircon U-Pb ages measured in situ by excimer laser ablation–inductively coupled plasma–mass spectrometry (ELA-ICP-MS) and verified by sensitive high-resolution ion microprobe (SHRIMP) on ore-bearing felsic porphyries from the Chuquicamata porphyry copper-molybdenum deposit, northern Chile, identify two discrete igneous events. The volumetrically dominant East porphyry has an age of 34.6 ± 0.2 Ma, whereas the Bench and West porphyries yield ages of 33.3 ± 0.3 Ma and 33.5 ± 0.2 Ma, respectively. The age of the East porphyry is indistinguishable from a Re-Os age for early molybdenite mineralization (35 Ma) and the oldest reported 40 Ar- 39 Ar ages for hydrothermal alteration, confirming a genetic link with mineralization. Previous geological studies and 40 Ar- 39 Ar and Re-Os geochronology identify two main hydrothermal events: high-temperature potassic alteration with chalcopyrite at 33.4 ± 0.3 Ma followed by lower temperature quartz- sericite alteration with pyrite at 31.1 ± 0.3 Ma. The ages of the West and Bench porphyries match the ages for potassic alteration. Younger quartz-sericite alteration may reflect an additional fourth intrusion concealed at depth. The anomalously large size of Chuquicamata appears to be due to a protracted igneous history resulting in the superposition of at least two temporally distinct magmatic-hydrothermal systems.

Re-Os AND U-Pb DATING OF THE VEIN-HOSTED MINERALIZATION AT THE KANSANSHI COPPER DEPOSIT, NORTHERN ZAMBIA

The Kansanshi copper deposit in the Pan-African Damaran-Lufilian fold belt of northern Zambia consists of high-angle, sheeted quartz-carbonate-sulfide veins with envelopes of disseminated sulfides. These veins cut and replace metamorphosed Katangan sedimentary rocks of Neoproterozoic age. Crosscutting relationships have been used to delineate three stages of subparallel veins. The first two vein sets are chalcopyrite rich and contain minor molybdenite, and the third vein set contains relatively abundant molybdenite with significant monazite and brannerite and minor chalcopyrite. Direct dating of molybdenite (with replicates) from each of the vein sets using the Re-Os method yields two distinct ages, 512.4 ± 1.2 Ma and 502.4 ± 1.2 Ma (weighted averages, 2 σ ), consistent with the relative age relationships and vein mineralogies observed in the field. The molybdenite-monazite veins, which crosscut the two earlier chalcopyrite-rich vein sets, are distinctly younger (~10 m.y.), based on Re-Os dating. SHRIMP U-Pb analyses of monazite from the final veining event yield a U-Pb age of 511 ± 11 Ma. The 2 σ uncertainty of ±11 m.y. includes all ages and 2 σ uncertainties provided by the Re-Os method. These results indicate that mineralization took place in the late Cambrian and suggest that either mineralization was continuous for 10 m.y. or the Kansanshi deposit includes two pulses of mineralization, one at ~512 Ma and one at ~502 Ma. Vein mineralogies and clear crosscutting relationships favor the latter suggestion. The ages of mineralization at Kansanshi are broadly similar to those determined for other posttectonic vein systems in the central African copper belt. Available geochronological data from deposits in the Damaran-Lufilian orogen suggest that a major mineralization event occurred throughout much of the Lufilian fold and thrust belt during and after peak metamorphism and that mineralizing fluids responsible for the formation of many of these deposits, including Kansanshi, may have been metamorphic in origin.

Hydrothermal alterations associated with Molybdenite mineralization in the

Hydrothermal alterations associated with Molybdenite mineralization in the

Hydrothermal Alteration and Fluid Chemistry of the Endako Porphyry Molybdenum Deposit, British Columbia

Hydrothermal alteration and fluid chemistry data of the early Cretaceous Endako porphyry molybdenum deposit, British Columbia, provide new information on the hydrothermal fluids associated with low-fluorine molybdenite mineralization. Molybdenite mineralization and hydrothermal alteration occur as early quartz ± molydenite stockwork veins with K feldspar-bearing selvages and paragenetically later quartz-molybdenite ribbon veins with sericite-bearing selvages. Late hydrothermal alteration is associated with the development of kaolinite and postore (Tertiary age) calcite veins. Fluid inclusions in early-formed quartz ± molybdenite stockwork veins with K feldspar-bearing alteration assemblages are dominated by moderate-salinity (5 to 15 wt % NaCl equiv), liquid-rich (type 1) and rare high-salinity (30 to 45 wt % NaCl equiv), halite-bearing (type 3) fluid inclusions. Type 1 and type 3 fluid inclusions in early veins homogenize between 390° and 430°C and 375° and 420°C, respectively. Secondary fluid inclusions (type 2) of low salinity (1 to 5 wt % NaCl equiv) in these early veins are minor, and homogenize between 130° and 285°C. Fluid inclusions in quartz-molybdenite ribbon veins with sericite-bearing alteration assemblages are dominated by moderate-salinity, liquid-rich (type 1) inclusions, with minor type 2 fluid inclusions. Type 1 fluid inclusions of ribbon veins homogenize between 360° and 400°C. Fluid inclusions in postore calcite veins are of only type 2 fluid inclusions, which homogenize at 209°C. Hydrothermal fluids recorded by type 1 and type 3 fluid inclusions in early veins were trapped under lithostatic to hydrostatic conditions between 0.3 and less than or equal to 2.0 kbar, and 360° and 560°C. Postore fluids recorded by type 2 fluid inclusions were trapped under conditions less than or equal to 0.5 kbar, and between 190° and 300°C. Quartz stockwork and ribbon veins possess δ 18O values of 8.4 ± 0.2 ( n = 9) and 8.4 ± 0.6 ( n = 13), respectively. Hydrothermal K feldspar and biotite from K feldspar alteration assemblages possess δ 18O values of 6.8 ± 0.4 ( n = 7) and 3.5 ± 0.8 ( n = 8), respectively. Oxygen isotope geothermometry of quartz-biotite and quartz-K feldspar pairs from K feldspar alteration assemblages yield temperatures between 200° and 490°C, which is similar to the trapping temperatures of hydrothermal fluids determined from fluid inclusion studies associated with molybdenite mineralization, the development of kaolinite, and calcite veins. The oxygen isotope temperatures of the quartz-biotite and quartz-K feldspar pairs suggest that K feldspar and biotite either record the approximate 18O composition of hydrothermal fluids associated with K feldspar alteration or have undergone 18O exchange with late-stage hydrothermal fluids. Hydrogen isotope composition of quartz stockwork and ribbon veins fluid inclusion waters range between –105 and –173 per mil. Solute chemistry studies of fluid inclusion waters indicate that ore-forming fluids from Endako have low Br/Cl and Br/Na ratios, and high I/Cl and I/Br ratios in comparison to Porgera (epithermal), Babine Lake (porphyry Cu), and St. Austell, Capitan Pluton (vein) deposits associated with magmatic processes. Na/K ratios of fluid inclusion waters yield temperatures (308° to 429°C) similar to those determined from type 1 and type 3 fluid inclusions and stable isotope thermometry. Results from fluid inclusion and solute chemistry studies indicate the involvement of hydrothermal fluids exsolved from a crystallizing melt in the formation of the Endako molybdenum deposit. However, oxygen and hydrogen isotope values deviate from the generally accepted magmatic compositions, which suggests the early involvement of meteoric water in the ore-forming fluids and ore genesis.

Experimental alteration of molybdenite: evaluation of the Re–Os system, infrared spectroscopic profile and polytype

Experiments have been carried out to clarify the effect of alteration on Re–Os system, near infrared (NIR)–infrared (IR) spectroscopic characteristics and polytype of a natural molybdenite mineral (MoS 2). The molybdenite sample was placed in H 2O and various media of 0.1 mol/L NaCl, NaHCO 3, CaCl 2, and AlCl 3 solutions, and heated in a sealed quartz tube at a temperature of 180°C for 20 d. The unaltered and altered samples were subsequently used for analysis of Re and Os, NIR microscopic observation, and NIR–IR spectroscopy, and microfocus X-ray diffraction (XRD). Molybdenites subjected to NaCl and NaHCO 3 solutions give younger Re–Os ages than that of the original unaltered molybdenite. No significant changes in d spacing and width of micro-XRD patterns can be found in these altered molybdenite, indicating the possibility of Re–Os fractionation without significant structural conversion of molybdenite mineral. These results strongly suggest that the Re–Os system in molybdenite would be frequently disturbed if it has experienced alteration, because alteration by the low salinity (<1%), low temperature (∼180°C) hydrothermal solution containing NaCl and/or CO 2 is commonly found in the natural environment. We maintain, therefore, that one set of analyses of Re and Os in a sample is not enough to determine whether the obtained Re–Os age has been affected by postdepositional alteration, but systematic replicate analyses are indispensable. Additionally, pulverizing all the collected molybdenite in a sample might give misleading results because portions, which have been altered and experienced Re–Os fractionation, may possibly mix into the undisturbed sample and be homogenized. The molybdenite used for the experiment was originally opaque under NIR light. Infrared microscopic and spectroscopic profiles show that some parts of the molybdenite subjected to CaCl 2 and AlCl 3 solutions become transparent to NIR. Increased NIR transmittance is possibly attributed to the removal of the impurity band in molybdenite. It was also found in this study, however, that change in IR profile does not correlate with the Re–Os fractionation and, therefore, IR measurement solely is not useful to detect disturbance of Re–Os systematics of molybdenite in alteration.

Fluid regime and ore formation in the tungsten(–yttrium) deposits of Kyzyltau (Mongolian Altai): evidence for fluid variability in tungsten–tin ore systems

The Kyzyltau ore field is located in the northern part of the Mongolian Altai Mountains. W(–Y–Be–Mo) mineralization occurs in veins and stockworks in granites, felsic volcanics, basaltic flows, and conglomerates. The main ore minerals in the veins are wolframite, fluorite, beryl and minor molybdenite. Inclusions in hydrothermal quartz, fluorite and beryl from veins, as well as in magmatic quartz in vein-hosting granites of the Ulaan uul, Buraat uul and Tsunkheg deposits were investigated using microthermometry and laser Raman spectroscopy. Pseudosecondary/primary inclusions in the Kyzyltau ore veins are predominantly liquid-rich aqueous inclusions, containing variable amounts of CO 2 as the main gas component, and showing N 2/CH 4 ratios >1. Secondary inclusions contain no or only trace concentrations of gases, as indicated by clathrate melting. The T h values of pseudosecondary/primary inclusions in veins are between 180 and 433°C. Fluid inclusion data indicate that phase separation processes leading to fluid immiscibility occurred in vuggy quartz II and green fluorite II in the Ulaan uul and Buraat uul ore veins. Phase separation pressures of 100–350 bars were estimated. Fluorite I from the Kyzyltau ore field shows a strong enrichment of HREE and a strong negative Eu anomaly common for rare metal-bearing ore systems. Fluorite II from Buraat uul and Tsunkheg is characterized by a change in the incorporation of rare earth elements (REE) with decreasing HREE contents and a decreasing Eu anomaly. The REE distribution patterns in fluorite II from Ulaan uul remained unchanged compared with fluorite I despite a strong increase in the total REE content. A review of the literature shows that from high-temperature, Fe-rich, K-dominated brines cassiterite ores can precipitate in quartz veins together with Fe–chlorite and Fe–tourmaline (Bolivian type). If phase separation of a gas-rich, low-salinity and Fe-rich fluid occurs, cassiterite–wolframite ores may be deposited (Cornwall/Devon type). The deposits of Kyzyltau are characterized by low-Fe alteration assemblages, a predominance of sodium over potassium, high contents of REE and Y, and a lack of extended tin mineralization despite the tin potential of the ore systems. Fluid inclusion data as well as geochemical and geological indications suggest formation of the tungsten deposits near the tops of Li–F-rich sub-volcanic intrusions. We interpret the pH of the mineralizing fluid to be the main factor controlling wolframite precipitation in the Kyzyltau ore field. Fluid–wall rock interactions, a lowering of the temperature and unmixing processes in the ore fluid generated contributions to neutralization and buffering of the acid CO 2-bearing fluid into a pH range where tungstates were precipitated. It can be inferred that formation of tungsten ores without precipitation of extended tin mineralization is possible in deposits characterized by high potential tin and tungsten. According to this inference, tin mineralization may be found in a more favourable setting in the vicinity of the Kyzyltau deposits.

Nature, origin and evolution of the granitoid-hosted early Proterozoic copper-molybdenum mineralization at Malanjkhand, Central India - a reply

At Malanjkhand, Central India, lode-type copper (-molybdenum) mineralization occurs within calcalkaline tonalite-granodiorite plutonic rocks of early Proterozoic age. The bulk of the mineralization occurs in sheeted quartz-sulfide veins, and K-silicate alteration assemblages, defined by alkali feldspar (K-feldspar ≫ albite) + dusty hematite in feldspar ± biotite ± muscovite, are prominent within the ore zone and the adjacent host rock. Weak propylitic alteration, defined by albite + biotite + epidote/zoisite, surrounds the K-silicate alteration zone. The mineralized zone is approximately 2 km in strike length, has a maximum thickness of 200 m and dips 65°–75°, along which low-grade mineralization has been traced up to a depth of about 1 km. The ore reserve has been conservatively estimated to be 92 million tonnes with an average Cu-content of 1.30%. Supergene oxidation, accompanied by limited copper enrichment, is observed down to a depth of 100m or more from the surface. Primary ores consist essentially of chalcopyrite and pyrite with minor magnetite and molybdenite. δ34S (‰) values in pyrite and chalcopyrite (−0.38 to +2.90) fall within the range characteristic of granitoid-hosted copper deposits. δ18O (‰) values for vein quartz (+ 6.99 to +8.80) suggest exclusive involvement of juvenile water. Annealed fabrics are common in the ore. The sequence of events that led to the present state of hypogene mineralization is suggested to be as follows: fracturing of the host rock, emplacement of barren vein quartz, pronounced wall-rock alteration accompanied by disseminated mineralization and the ultimate stage of intense silicification accompanied by copper mineralization. Fragments of vein quartz and altered wall rocks and striae in the ore suggest post-mineralization deformation. The recrystallization fabric, particularly in chalcopyrite and sphalerite, is a product of dynamic recrystallization associated with the post-mineralization shearing. The petrology of the host rocks, hydrothermal alteration assemblages, ore mineral associations, fluid inclusions and the sulfur and oxygen isotopes of ores are comparable to those in Phanerozoic (and reported Precambrian) porphyry-copper systems, and the Malanjkhand deposit has important implications for both metallogenic models for, and mineral exploration in, Precambrian terrains.

Reduction and Immobilization of Molybdenum by Desulfovibrio desulfuricans

The mobility of Mo in the environment is strongly dependent on its chemical oxidation state. Under oxidizing conditions, Mo occurs as highly soluble and mobile Mo(VI) and Mo(V) compounds. However, under reducing conditions Mo usually forms insoluble Mo(IV) phases. The objective of this study was to demonstrate the ability of the sulfate-reducing bacterium, Desulfovibrio desulfuricans, to reduce Mo(VI) to Mo(IV) in anaerobic environments. Molybdenum-VI was reduced to Mo(IV) by washed cells of desulfuricans suspended in bicarbonate buffer solution with either lactate or H 2 as the electron donor and Mo(VI) as the electron acceptor. Molybdenum-VI reduction by D. desulfuricans in the presence of sulfide resulted in the extracellular precipitation of the mineral molybdenite [MoS 2(s) ]. Molybdenum-VI reduction did not occur in the absence of an electron donor or in the presence of heat-killed cells of D. desulfuricans. Attempts to grow D. desulfuricans with Mo(VI) as the sole electron acceptor were unsuccessful. Direct chemical reduction of Mo(VI) by sulfide or by H 2 was also unsuccessful, even when heat-killed cells of D. desulfuricans were added to provide a potential catalytic surface for the nonenzymatic reaction. Desulfovibrio vulgaris reduced Mo(VI)to Mo(lV) equally well. The results indicate that enzymatic reduction of Mo(VI) by sulfate-reducing bacteria may contribute to the accumulation of Mo(lV) in anaerobic environments and that these organisms may be useful for removing soluble Mo from contaminated water.

Chiral symmetry breaking during the self-assembly of monolayers from achiral purine molecules.

Scanning tunneling microscopy was used to investigate the structure of the two-dimensional adsorbate formed by molecular self-assembly of the purine base, adenine, on the surfaces of the naturally occurring mineral molybdenite and the synthetic crystal highly oriented pyrolytic graphite. Although formed from adenine, which is achiral, the observed adsorbate surface structures were enantiomorphic on molybdenite. This phenomenon suggests a mechanism for the introduction of a localized chiral symmetry break by the spontaneous crystallization of these prebiotically available molecules on inorganic surfaces and may have some role in the origin of biomolecular optical asymmetry. The possibility that purine-pyrimidine arrays assembled on naturally occurring mineral surfaces might act as possible templates for biomolecular assembly is discussed.

The metamorphosed molybdenum vein-type deposit of the Alpeinerscharte, Tyrol (Austria) and its relation to Variscan granitoids

The molybdenite deposit of the Alpeinerscharte (Austria) is situated in Variscan greenschist- to amphibolite-facies metamorphosed granodiorites and granites of the western Tauern Window. These granitoids represent strongly fractionated calc-alkaline I-type magmas with minor S-type components and reveal post-orogenic affinities. Molybdenum contents (average 4.3 ppm) are slightly above the general background of average granites. Molybdenite mineralization is restricted to narrow quartz veins and quartz vein selvages which are presently composed of biotite and (almandine-grossular) garnet. These selvages show geochemical features typical of intermediate argillic alteration in a hydrothermal system postdating granite intrusion: instability of plagioclase causes removal of Na, Ba, Sr, Pb and Eu, while K and Ca remain nearly constant. Rare earth elements (apart from Eu) and metals are extremely enriched. Application of Fe-Mg exchange (garnet-biotite) and oxygen isotope (quartz-garnet, quartz-plagioclase) geothermometers to vein selvage mineral assemblages reveals temperatures of the late-Alpine (35–55 Ma) metamorphic overprint (∼540°C, 7–10 kbar). Leucocratic rocks composed of mainly orthoclase and plagioclase are occasionally spatially related to molybdenite-bearing veins; they are interpreted as episyenites formed by hydrothermal alteration of the host granite. This episyenitic alteration is characterized by a mass loss of ca. 30%, relative enrichment of plagioclase components, extreme depletion of Si, and minor depletion of Fe, Zn, Cu and Mo.

Comparison of methods used to inhibit bacterial activity in sulfide ore bioleaching studies

Eight methods of ore sterilization, including steam autoclaving, dry heat, tyndallization, cobalt-60 irradiation, thymol (5-methyl-2-(1-methylethyl) phenol) and mercuric chloride additions, were tested using a monzonite porphyry copper ore containing chalcocite, chalcopyrite, pyrite, and minor molybdenite. All treatments were found to effectively eliminate iron-oxidizing bacteria added to the ore. Heating methods were found to be effective sterilization procedures and to have a minimal influence on the leaching characteristics of the ore. However, gamma irradiation and the additions of thymol and mercuric chloride significantly altered the ore and suppressed the abiotic leaching rate. Results suggest that previous bioleaching studies using thymol as a bacterial inhibitor may have overestimated the bacterial role in ore leaching.

Direct evolution of brine from a crystallizing silicic melt at the Questa, New Mexico, molybdenum deposit

Molybdenum mineralization in the Southwest orebody at the Questa deposit is associated with crystallization of aplite porphyry, explosive brecciation, and exsolution of magmatic hydrothermal fluids. Quartz, K feldspar, fluorophlogopite, and molybdenite precipitated from exsolving aqueous fluids and cemented aplite porphyry and andesite wall-rock clasts forming a magmatic hydrothermal breccia ore.Fluid inclusions in quartz in the breccia matrix trapped aqueous fluids that transported and precipitated molybdenum. Two fluid inclusion populations associated with molybdenite mineralization were identified. The largest population commonly contains liquid, vapor, halite, sylvite, and one or more opaque daughter crystals. These inclusions homogenize between 200 degrees and 500 degrees C and have a prominent mode at 360 degrees to 400 degrees C; salinities vary from 31 to 57 wt percent NaCl equiv. Low first ice-melting temperatures suggest that additional fluid components, possibly calcium or magnesium chlorides, may be present. Approximately 80 percent of these inclusions homogenize by halite dissolution; phase equilibria constraints require that these inclusions trapped fluids in the vapor-absent field. The remaining saline inclusions homogenize to liquid at temperatures above halite dissolution temperatures. Significantly, the saline fluid did not coexist with a low-density aqueous fluid.A second population of inclusions contains fluids with salinities of 2.7 to 25.0 wt percent NaCl equiv and homogenizes by vapor bubble disappearance, vapor bubble expansion, or critical behavior. Textural relationships and phase behavior during microthermometry indicate that these inclusions constitute a single population which formed as pressure and temperature fluctuated at near-critical conditions.Pressure changes related to brecciation followed by crystallization and system resealing produced the observed fluids. Saline fluids were trapped as the system sealed following a major brecciation event. These high-salinity fluids were produced as the melt, under pressure that increased from hydrostatic to lithostatic, partitioned increasing amounts of chlorine into the exsolving aqueous fluid. Renewed fracturing and abrupt pressure decrease to hydrostatic conditions reduced the mass of chlorine partitioning to the exsolving fluid. Lower salinity fluids exsolved at near-critical conditions and were trapped by inclusions that homogenize to liquid, to vapor, or by critical behavior. The lack of cogenetic liquid- and vapor-rich fluid inclusions and phase equilibria constraints indicate that high-salinity fluids (< or = 57 wt % NaCl equiv) were generated directly by the crystallizing magma and were not a product of aqueous fluid immiscibility.

Partial Melting Features of Metamorphosed Ores from Rangpo Polymetaltic Deposit (Sikkim, India)

Investigation of metamorphosed; ores is especially in teres t ing because of cur rent th inking (Mookcherjee, 1967; Parilov, 1984; Starostin, et al., 1990) on possibility of appearance of sulphide melts due to metamophism of ores. Samples of metamorphosed ore from Rangpo polymetallic deposit have been studied by means of ore microscopy and EPMA. Sphalerite, pyrrhotite, chalcopyrite, magnetite, arsenopyrite and Co-sulpharsenides are the main ore minerals in the samples studied. Pyrite, galena and Agfahlores are less abundant. Rare minerals molybdenite, sulphosalts and native Bi and Ag. The ore minerals are intimately interlocked with silicate gangues (garnet, orthorhombic pyroxene, amphibole and others). The interesting features of the ore are as follows: 1. Oblong shape of sphalerite grains subordinating to schistosity of slates; 2. Absence of chalcopyrite and/or pyrrhotite emulsion inclusions in sphalerite and vica versa star-shaped inclusions of sphalerite; 3. Abundant postmetamorphic appearance of magnetite, capturing pyrrhotite layers in schistose textures of ore; 4. Droplets of chalcopyrite-pyrrhotite inclusions in magnetite porphyroblasts and numerouse droplets of non-opaque inclusions in pyrrhotite grains; 5. Myrmekitic (eutectic) intergrowth of predominant galena with the lesser Ag-tetrahedrite, native Bi and pyrrhotite, occuring among the big grains of sphalerite and magnetite; 6. Filling the cricks in garnet idiomorphic grains by magnetite and sulphides without conducting veinlets and noticeable corrosion of the garnet grains; 7. Zonal rhombic-shaped crystals of Co-sulpharsenide, formed by alternating zones of sulpharsenides and galena without conducting veinlets of galena; 8. Finding of new unusual complex sulphide ('mineral G') CusFe6(Pb6(Bi,Sb,As)2(S,Se,Te)21; 9. Absence of isomorphic Agand Bi-impurities in galena. These features of the Rangpo ores resemble those which are formed in smelting products in furnaces. According to Edwards (1954), magnetite crystals are the common product of many mattes, speisses and slags; magnetite in slags often contains droplets of different substances (e.g. Cu-sulphides); eutectic intergrowths, formed by Pband Cu-sulphides, occupy small intersticial areas in the smelting products; a complex Cu-AsSb compound, which may be conpared with 'mineral G' from Rangpo, was observed in the matte containing semi-metals. Such resemblance permits to think that partial melting of ore minerals took place during metamorphism of the Rangpo ores. This point of view agrees with experimental works (Brett and Kullerud, 1966; Lowrence, 1967). According to these works, partial melting of sulphides may occur at temperatures around 700~ Lowrence indicated, the presence of fluxes (water vapour, fluorine and others) may significantly lower the melting point of Pb-Zn-sulphide

Whole-rock geochemistry and fluid inclusions as exploration tools for mineral deposits assessment in the Serre batholith, Calabria, southern Italy

Field and geochemical studies of granitic plutons belonging to the Serre batholith, in southern Calabria, show that some of these plutons are associated with minor molybdenite, base-metal occurrences, and granitophile geochemical anomalies. The results of a geochemical survey of granitic bedrock and treatment of the data by statistical techniques indicate a grouping of geochemically anomalous samples, with clusters of high R-mode factor scores that identify potential hosts of significant granite-related mineralization, especially Mo, Sn, and W. Especially favourable hosts are siliceous and generally potassic differentiated granitic rocks, especially near the village of San Todaro, and near Bagni di Guida, Monte Cola, Monte Crocco and Mongiana. These areas are candidates for more detailed exploration, as they contain clustering of significant geochemical anomalies for Mo, Rb, W, Cu, Nb, etc., and more importantly, these granites are known to host base-metal sulphide veins. Granite specialization indices for (Rb/Sr>5, K/Rb 0.1) are also typical of granitic rocks hosting base-metal and granitophile mineralization; high-factor scores for the associations K-Rb-Ba-Al-Pb, Nb-Sn, Sn-As and Cu-Sn are also found. Intrusive rocks from the Serre batholith, and from the nearby Sila batholith, in northern Calabria, have similar fluid inclusion features; both contain fluid inclusions that resemble those from granites known to show mineralization elsewhere. A common characteristic of inclusions in Sn-bearing granitic rocks and those in the Serre batholith is the correlation between homogenization temperature and salinity, suggesting mixing of magmatic saline fluids with cooler, lower salinity meteoric waters. There is no evidence, however, that vigorous, voluminous, and intense alteration by boiling and high salinity hydrothermal systems were developed in the Serre batholith. Sulphide-bearing veins near Bagni di Guida and San Todaro, two of the most important areas identified in this study as potential hosts, probably reflect episodic tectonic adjustments that momentarily dropped the pressure from lithostatic to hydrostatic, producing boiling and minor hydrothermal alteration. Known sulphide occurrences in the Serre batholith are thus unlikely to be expressions of a major hydrothermal alteration and mineralization system, unless the occurrences represent the distal effects of such a system

Determination of osmium abundance in molybdenite mineral by isotope dilution mass spectrometry with microwave digestion using potassium dichromate as oxidizing agent

An efficient and reliable method was developed for the accurate determination of osmium abundance in molybdenite (MoS2) by isotope dilution mass spectrometry. The sample solution of molybdenite was prepared by acid decomposition using the microwave digestion technique with addition of potassium dichromate (K2Cr2O7) as oxidizing agent and osmium in the sample solution was purified by distillation. There was no change in the ratios of 187Os derived from molybdenite relative to 192Os of an osmium standard with progress of distillation, indicating that isotopes of osmium derived from the two sources were completely homogenized. The precision of the osmium abundance obtained in the developed method was 1%(1σ). The technique was applied to a natural molybdenite sample for Re—Os age determination and the result was in good agreement with that obtained by the U—Pb method for zircon.

Ore reserve estimation in Los Pelambres, A Chilean porphyry copper

Abstract Los Pelambres is a world-class Chilean porphyry copper orebody located in the Andes Range adjacent to the border with Argentina at an elevation of 3100 m. It is characterized by a stock-size Tertiary granodiorite complex intruding a lower Cretaceous volcano-sedimentary sequence. Several multi-episodic stages of hypogene alteration and mineralization related to late porphyries and hydrothermal breccias occur, as well as secondary enrichment, generating a well defined orebody with bornite-chalcopyrite-chalcocite as the main copper minerals with minor molybdenite. Additionally, some gold and silver values are present. Grade zoning and kriging methods have been used to evaluate the richest east portion of Los Pelambres.

Sulphur-isotope and elemental geochemistry studies of the Hemlo gold mineralization, Ontario: sources of sulphur and implications for the mineralization process: Discussion

Undoubtedly, geochemical studies can provide key information on the genesis of an ore deposit but it is important to constrain these studies by reliable ore paragenesis. This is particularly important for the Hemlo gold deposit, which is characterized by a long history of deformation and metamorphism. In their paper the authors have used sulfur-isotope studies to determine the temperature of isotopic equilibrium and to speculate on the possible source of sulfur of barite and sulfides. In our opinion the methodology of their study is very questionable because they seem to give no consideration to the ore paragenesis and the relative timing of deformation, metamorphism, and gold mineralization. In the Golden Giant mine Michibayashi (1991) has recorded the presence of two distinct types of barite: highly folded and sheared-banded barite and massive barite filling fractures within the feldspathic-altered ore bodies. The massive barite appears to have formed after the potassic alteration as a result of syntectonic remobilization of the banded barite. The massive barite is characterized by microstructures (polygonal to dynamically recrystallized) indicating that barite was deformed plastically. Based on the mesoscopicand microscopic-scale structures the pyrite grains can be divided into three types: sub to euhedral pyrite, polygonal pyrite, and elongate pyrite with their long axes parallel to the schistosity. Onetching, the individual pyrite grains commonly show zoned structure with a core overgrown by a later generation of possibly metamorphic pyrite. In the Golden Giant mine, microstructural studies reveal a difference in the timing of formation of molybdenite and stibnite. molybdenite has formed synchronously with the development of S, and S, cleavages and was associated with the formation of potash-feldspar and muscovite. Stibnite occurs along rnicrofractures that cut across both S, and S, cleavages and is coeval with the development of S, (Michibayashi 1991). Gold is associated with both molybdenite and stibnite mineralization and appears to be unrelated to barite. The authors have used the equilibrium fractionation between barite and pyrite to determine the temperature. According to them, the temperatures determined by sulfur-isotope fractionation (varying between 492 and 557°C) are close to those determined by the oxygen-isotope fractionation between quartz and muscovite, although the oxygen-isotope geothermometer

Acdidophilic thermophilic archaebacteria: Potential application for metals recovery

The acidophilic thermophilic archaebacteria Sulfolobus and Acidianus have the potential for applid use in the recovery of metal values from ores through the process of baterial leaching. These microbes readily adapt to the conditions of low pH and high concentrations of metals required for bacterial leaching. In addition, these archaebacteria can exist at high temperatures which can occur during the oxidation of metal sulfides in bioleaching reactors. The acidophilic of copper and molybdenum from chalcopyrite and molybdenite minerals, respectively. The microbes can also enhance the recovery of gold by oxidation of pyrite which occludes gold preventing recovery by standard metallurgical procedures. The ability of this group of microbes to facilitate metals recovery is yet to be developed on a commercial scale.

Acdidophilic thermophilic archaebacteria: Potential application for metals recovery

The acidophilic thermophilic archaebacteria Sulfolobus and Acidianus have the potential for applid use in the recovery of metal values from ores through the process of baterial leaching. These microbes readily adapt to the conditions of low pH and high concentrations of metals required for bacterial leaching. In addition, these archaebacteria can exist at high temperatures which can occur during the oxidation of metal sulfides in bioleaching reactors. The acidophilic of copper and molybdenum from chalcopyrite and molybdenite minerals, respectively. The microbes can also enhance the recovery of gold by oxidation of pyrite which occludes gold preventing recovery by standard metallurgical procedures. The ability of this group of microbes to facilitate metals recovery is yet to be developed on a commercial scale.