Main Orebody Research Articles

Analysis of the Regularity and Mechanism of Fault Activation Caused by Deep Continuous Mining of Shizishan Copper Mine, China

In order to study the law and mechanism of fault activation induced by deep continuous mining, this paper takes the fault activation caused by underground mining of Shizishan Copper Mine as the research object. On the basis of field investigation and theoretical analysis of fault activation, the law and mechanism of fault group activation induced by deep continuous mining in the Shizishan mining area are analyzed in detail based on the three-dimensional discrete element method software 3DEC. The results show that the fault effect of rock movement in the footwall of the main orebody in the mine area is obvious. The en echelon steep dipping fault group in the footwall of the goaf will move each fault block in the direction of the goaf and slip along the fault plane when the balance between mining and gravity is disrupted. The fault activation has a domino effect in time and space, and the mechanism of this effect is revealed. The research results have great significance for the deep mining area development, mining alignment arrangement, and disaster prevention and control caused by fault activation.

Monitoring and Analysis of Deformation Evolution Law of Fault Activation Caused by Deep Mining in Shizishan Copper Mine, China

In order to study the deformation evolution law of fault activation caused by deep mining in Shizishan Copper Mine, China, a monitoring system for fault activation slip is designed and implemented on the basis of the field investigation of footwall fault activation of the main orebody in the mining area. The displacement and stress of the fault are monitored by the multipoint displacement meter, bolt stress meter, and borehole stress meter. According to the measured results, the activation deformation laws of fault F2, fault F3, and fault F4 during deep continuous mining are analyzed in detail. The results show that, when the influence range of underground mining spreads to the fault, the increase in the additional tensile stress on the fault plane will reduce the shear strength of the fault and increase the slip of the fault. When the shear stress exceeds the shear strength of the fault plane, the shear failure of the fault plane occurs, the rock mass on both sides of the fault loses stability, and the fault becomes active; when the orebody in the deep sublevel 14 and sublevel 15 were continuously stoped, the development of the mining influence area to fault F2 leads to fault F2’s activation. When stoping the orebody in sublevel 16, fault F3 also activates. With the continuous downward mining of the deep part, the slip amount increases continuously. The fault activation sequence is from fault F2 to fault F3, and then to fault F4.

Investigation of the effects of rock dynamic hardness on the energy consumption in the crushing unit, case study: Midouk copper mine

ABSTRACT The mounted semi autogenous (SAG) mill in the processing unit of the Midouk copper mine which consumes 35% of operational costs has a critical size within the range of 2.5–5 cm. To optimize the energy consumption in the milling unit of the mine, the data have been collected from 36 blast blocks. These blocks are selected in the main ore body area to monitor their effects on energy consumption in the milling unit. Owing to the dependence of mill energy consumption on the feed strength properties, a criterion for mill performance (MPC) has been defined and compared with the obtained dynamic hardness of seven specific blasting blocks. The results show a linear relationship with the accuracy of R 2 = 0.91 between the dynamic hardness and the MPC. For mines that use SAG or AG mills, the energy consumption for crushing the unit weight of feed depends on their dynamic stiffness.

Principles governing the selection of ore regions for gold deposit search

Background. In 2020, the Auditing Chamber of the Russian Federation, based on a representative report by its expert analysts M. Men’ and A. Kaulbars, proposed expanding the search for deposits of a number of metals, including gold. Since the fund of easily discovered gold deposits coming to the surface has been significantly reduced, prospecting of ore regions most promising in terms of gold deposits becomes highly relevant.Aim. In connection with the above task, it seems expedient to outline territories within the currently known gold provinces, where the prerequisites and signs of gold ores could be detected with minimal expenditures for their subsequent verification by drilling.Materials and methods. The study involved calculating the shares of the world’s gold reserves attributable to each type of distinguished deposits located in various rocks. The extensive experience of prospecting work carried out in recent decades and culminated in the discovery of the Muruntau deposit in Uzbekistan, a world leader in the development of gold deposits, and Russian largest and giant deposits – Natalka, Sukholozhskoe, Nezhdaninsky, Degdekansky, Maisky, Oktyabrsky, Pavlik, Kupol, as well as the Bakyrchik deposit in Kazakhstan and others, clearly shows that the most promising and largest deposits are selectively localized in favourable rocks and largescale disjunctive dislocations, or faults. To identify favourable rocks, the distribution of the world’s gold reserves in various rocks was analysed, as well as the distribution of reserves in the areas of the largest deposits in ore-bearing faults as the most favourable fault types containing the most powerful and extended gold ore bodies.Results. A comparison of the shares of reserves has shown that the most promising for prospecting are those rock complexes containing the highest proportions of the world’s gold reserves. The article presents the distribution of shares of the world’s gold reserves for near surface and deep-formed deposits of various types. The main share of the world’s gold reserves in deeply formed deposits is shown to be concentrated in the Phanerozoic strata of sandy-clayey composition and in the interlayers of easily replaceable carbonate and amphibolite shales developed in the Proterozoic quartzite-phyllite rocks. The reserves of near-surface gold-silver and gold-telluride ores are selectively located in the young Mesozoic-Cenozoic volcanic rocks of basalt-andesite composition, accompanied by dikes, subvolcanic stocks and the pipes of explosive breccias with large-scale gold ore bodies confined to them. Thus, the most promising areas for prospecting new deposits are those composed of the mentioned rock complexes and crossed by ore-bearing faults, in the zones of which the main largest ore bodies are concentrated. Conclusion. The conducted study into the distribution of the world’s gold reserves in the deposits of various types, as well as the selective localization of ores in deposits with the main and large scale ore bodies in the zones of ore-bearing faults (and, accordingly, containing the concentration of the main share of reserves in a particular deposit), provides a basis for discovering new deposits of the precious metal with minimal expenditures, thus contributing to increasing the resource base of the Russian Federation.

Hydrous Juvenile Lower Crust at the Western Yangtze Craton Margin as the Main Source of the Beiya Porphyry‐skarn Au Deposit

AbstractThe Beiya porphyry‐skarn Au deposit is one of the largest gold deposits in China, temporally and spatially associated with Eocene intrusions in a post‐collisional setting in western Yunnan, China. In this study, we report new whole‐rock geochemistry, Sr‐Nd isotope, zircon U‐Pb geochronology and in situ zircon Hf‐O isotopes of quartz‐monzonite and biotite‐monzonite porphyries from the Beiya deposit. The porphyry‐skarn mineralization at the Beiya deposit is mainly associated with the quartz monzonite porphyry (35.8 ± 0.6 Ma), while the biotite‐monzonite porphyry (34.3 ± 0.5 Ma) represents a post‐mineralization intrusion crosscutting the main orebodies and the quartz‐monzonite porphyry. Both intrusions have high‐K and adakitic composition and are characterized by high Sr/Y ratios, high SiO2 and Al2O3 concentrations (SiO2 = 69.80–73.86 wt%; Al2O3 = 14.11–15.19 wt%), and low MgO, Cr, and Ni concentrations (MgO = 0.2–1.0 wt%; Cr = 1.76–11.13 ppm; Ni = 2.52–11.72 ppm). Their Sr‐Nd isotope compositions (87Sr/86Sr = 0.7066–0.7077; εNd(t) = –5.3 to –1.5) are consistent with the lower crustal‐derived amphibolite xenoliths (87Sr/86Sr = 0.7060–0.7100; εNd(t) = –10.0 to 0.0), indicating that they might be derived from a thickened juvenile lower crust beneath the Yangtze Craton. The biotite‐monzonite porphyry has lower zircon δ18O values of +5.3‰ to +6.8‰ and higher εHf(t) values of –2.3 to +5.5 than those of the quartz‐monzonite porphyry with δ18O values of +7.1‰ to +8.2‰ and εHf(t) values of –3.8 to +1.5, implying that they were derived from different parts of the lower crust. High Ba/La and Pb/Ce ratios suggest that the quartz‐monzonite porphyry is derived from a volatiles‐rich reservoir. Relatively higher La/Yb, Sm/Yb and Dy/Yb ratios of the biotite‐monzonite porphyry indicate residual garnet in the source, indicating a deeper source than that of the quartz‐monzonite porphyry. The hydrous components should be represented by the amphibole‐rich lithologies, which has relatively shallower depth than that of the garnet‐bearing mafic thickened lower crust. Our data suggest that the mineralized quartz‐monzonite porphyry at the Beiya deposit is derived from partial melting of amphibole‐rich lithologies in the upper part of the thickened juvenile lower crust beneath the Yangtze Craton, while the post‐mineralization biotite‐monzonite porphyry is derived from the basal, and volatiles‐poor, part of the juvenile lower crust.

High-Precision Joint Magnetization Vector Inversion Method of Airborne Magnetic and Gradient Data with Structure and Data Double Constraints

Airborne magnetic and gradient measurements are commonly used geophysical remote sensing tools to obtain the distribution features of ore mineral bodies. It is known that ore mineral bodies generally contain remanent magnetization, and magnetization vector inversion (MVI) can produce the magnetization intensity and direction of the source, which is more suitably used to interpret measured airborne magnetic and gradient data. To accurately reveal the underground magnetization vector distribution, we proposed a high-precision method with double constraints on the data and physical structure, and we used the cross-gradient inversion of airborne magnetic anomalies and the combination matrix of airborne magnetic and gradient (CMG) data to recover the physical parameters of the sources with different depths. We used the combination matrix to produce the different component data constraints and the cross-gradient function to finish the inversion to provide structural constraints. For anomaly sources at similar depths, joint inversion based on the cross-gradient of magnetic gradient data and CMG data is more suitably used. The superiority of the double constraints method is proven by theoretical model tests. We apply the proposed method to interpret airborne magnetic and gradient data in Shandong Province to detect iron mineral resources, and we select the cross-gradient inversion of airborne magnetic anomalies and CMG data depending on the nonlinear features of the power spectrum. The main ore bodies have a northeast distribution with a depth range of 1048–1800 m, successfully giving the distribution range of the high-magnetic bodies; a better mineral potential is in the northern part of the survey area.

Epithermal Au–Ag–Se–Te Deposits of the Chukchi Peninsula (Arctic Zone of Russia): Metallogeny, Mineral Assemblages, and Fluid Regime

Abstract Numerous epithermal Au–Ag deposits and ore occurrences of the Chukchi Peninsula are localized in the Cretaceous Okhotsk–Chukotka (OCVB) continent-marginal and Late Jurassic–Early Cretaceous Oloi (OVB) island arc volcanic belts and in Early Cretaceous postcollisional volcanic troughs. Volcanotectonic depressions, calderas, and volcanic domes control the location of the deposits. The orebodies of the deposits are quartz–adularia veins, sometimes en-echelon ones forming extending vein zones, as well as isometric and linear stockworks. The auriferous veins of most deposits display complex breccia–crustification structures. The vein ores have rhythmically and colloform–banded structures, with a predominantly fine distribution of ore mineral grains, often with banded clusters of ore minerals (ginguro). Native gold is of low fineness; the dispersion of this index varies from low to high. Acanthite is widespread in the ores. Its highest contents are specific to deposits with the repeated redistribution of substance (Kupol, Corrida, and Valunistoe). Based on the results of mineralogical studies, most of the epithermal Au–Ag deposits of the Chukchi Peninsula can be assigned to the Se type. The ores of some deposits (Valunistoe, Dvoinoe, etc.) contain both Se and Te minerals. The telluride-richest sites of the Sentyabr’skoe and Televeem deposits are far from the main orebodies. Most of the Chukchi epithermal Au–Ag deposits have many common characteristics (low and moderate temperatures of fluids, low fluid salinity, domination of carbon dioxide over methane, etc.) typical of low-sulfidation deposits. The maximum temperatures and salinity are specific to fluids in the Central Chukchi sector of the OCVB and in the Baimka zone of the OVB, and the minimum ones are typical of fluids in the East Chukchi flank zone and inner zone of the OCVB. The average salinity of mineral-forming fluids in the inner zone of the OCVB is half as high as the salinity of fluids in the East Chukchi flank zone of this belt, although the sulfate content is higher. At the same time, the fluids in the inner zone of the OCVB are richer in carbon dioxide and bicarbonate ion than the fluids in the East Chukchi flank zone of this belt. The fluid inclusion data permit the Vesennee deposit (Baimka zone) to be regarded as an intermediate-sulfidation one and suggest the presence of epithermal high-sulfidation deposits in the inner zone of the OCVB.

Rare earth mining and consumption global trends and mining perspectives for the Mushugay Khudug deposit in southern Mongolia

In this work the 3 ore body drill core samples. 6 host rock samples from the main ore body of the Mushugay Khudug REE deposit in southern Mongolia were selected as most representative samples and studied by XRD and ICP-MS. LA-ICP-MS method to evaluate elemental and structural composition data of the deposit. According to our determinations the main orebody of the Mushugay Khuduk deposit contain up to 130 kg/ton of REEs. Despite the moderate total mineable reserve the main ore body of the Mushugay Khuduk deposit might compete economically with world's biggest REE mining deposits such as Bayan-Obo (Inner Mongolia. China) or Mountain Pass (California. USA) if consider the deposit's higher REE grade and easier to mine local geological condition. The important advantage of the Mushugay Khuduk deposit is that the relative contents of most valuable HREEs Eu. Tb. Dy. and Lu are significantly higher than that of Mountain Pass or Rayan-Obo. The relative net content of these four elements is 0.1% for Mountain Pass and 0.4% for Bayan-Obo. while the ore samples of the Mushugay Khuduk deposit has 0.75% according to our determinations.

Records of fluid-rock interactions in the Degana tungsten deposit, India: Inferences from mineral paragenesis, whole-rock and mineral chemistry, and fluid inclusions

The Degana Granite, a F-rich, peraluminous, Neoproterozoic intrusion in NW India hosts the richest tungsten deposit in the country. This study on the Degana W deposit outlines its alteration history, and nature (and evolution) of pre-ore and ore-stage fluids. Moderate salinity (5.4 to 9.6 wt% NaCl equiv.), H2O-CO2 fluids with nearly consistent CO2/(H2O + CO2) ratios of 0.05–0.07 represent the magmatic stage. A pervasive, post-magmatic K (±Na) alteration occurred in a fluid regime dominated by moderate salinity H2O-CO2 fluids. In subsequent alteration stages, the activity of greisen fluids led to the development of steeply-dipping quartz veins (poorly-mineralized), sub-parallel wolframite-bearing greisenized granitic wall-rock (main ore body), and and a late phase of stockwork-type greisen veins. The greisenization is attributed to the incursion of moderate to high salinity (12–22 wt%) H2O-CO2 ore fluids. Such fluids led to K-feldspar and muscovite hydrolysis, and the growth of lithian ferroan muscovite, secondary topaz, and wolframite (±cassiterite, fluorite). Greisenization introduced additional Fe and Li (+W, Sn) in the wall-rock zone and concomitantly leached out Na, K, Cu, Ba, Sr, U, Zr, and Th. Greisen fluids caused Fe leaching along with incorporation of Li in the micas. The compositions of tri- and di-octahedral micas are controlled by distinct substitution mechanisms --VILi1+1IVSi4+2VIAl3+1VIξ1VIFe2+-3IVAl3+-2, and VILi1+4IVSi4+1VIFe2+-1IVAl3+-1VIAl3+-1VIξ-2 (where ξ = vacancy), respectively. We constrain the P-T conditions of W enrichment (380–450 °C and 1.2–1.8 kbar) by means of isochore intersections for coexisting aqueous and carbonic fluid inclusions hosted in greisenized wall rock. The fall in pH of the ore fluid due to fluid-silicate hydrolysis in concomitance with H2O-CO2 immiscibility promoted the decrease in W solubility and subsequent wolframite precipitation. It is surmised that the pervasive, post-magmatic potassic alteration that preceded the ore mineralization acted as a critical pre-conditioning process for ore formation. Both tri- and di-octahedral micas were critical for W enrichment, the former being the likely source for Fe (+W, Sn), and the latter as a reactant for pH-neutralization of greisen fluid, thereby limiting its W solubility.

Compositions and Ni-Cu-PGE Tenors of Nova-Bollinger Ores with Implications for the Origin of Pt Anomalies in PGE-Poor Massive Sulfides

Abstract The Nova-Bollinger Ni-Cu-platinum group element (PGE) deposit in the Fraser zone of the Albany-Fraser orogen consists of two main orebodies, Nova and Bollinger, hosted by the same tube-shaped intrusion but having distinctly different Ni tenors of around 6.5 and 4.8 wt %, respectively. Nova is also higher in Pd, but Cu and Pt tenors are similar. Both deposits have very low PGE tenors, with average Pd concentrations of 110 ppb in massive sulfide at Bollinger and 136 ppb at Nova. The Nova and Bollinger orebodies show relatively little internal differentiation overall on deposit scale but show strong differentiation into chalcopyrite-rich and chalcopyrite-poor regions at a meter scale. This differentiation is more prevalent at Nova, where massive sulfide-filled vein arrays are more extensively developed, and in massive ores, particularly veins, than in net-textured ores. Net-textured and disseminated ores have on average Ni and Cu grades and tenors similar to those of massive, semimassive, and breccia ores in the same orebody but a smaller range of variation, largely due to a more limited extent of sulfide liquid fractionation and higher average concentrations of Pt and Pd than adjacent massive ores. Unusually for differentiated magmatic sulfides, there is no systematic positive correlation between Pt, Pd, and Cu. A partial explanation for the lack of a Pd-Cu correlation is that Pd was partitioned into peritectic pentlandite in the middle stages of sulfide liquid solidification. This explanation is not applicable to Pt, as Pt characteristically forms its own phases rather than residing in base metal sulfides. PGE tenors are very low in both orebodies, very similar to those observed in other Ni-Cu-Co sulfide ores in orogenic settings, notably the Savannah and Savannah North orebodies. This depletion is attributed to sulfide retention in the mantle source of the parent magmas rather than to previous fractional extraction of sulfide liquid in staging chambers or feeder networks. The higher Ni and Pd tenors at Nova are attributed to reworking and upgrading of precursor sulfide liquid originally deposited upstream at the Bollinger site. Replicate analyses of multiple jaw-crusher splits returned highly variable Pt and Au assays but much smaller relative errors in the other PGEs. The poor Pt and Au reproducibilities are attributed to nugget effects, explicable by much of the Pt and Au in the samples being present in sparse Pt- and Au-rich grains. This is principally true for Pt in massive rather than disseminated ores, accounting for a strong contrast in the distribution of Pt/Pd ratios between the two ore types. Numerical simulation suggests that Pt is predominantly resident in Pt-rich platinum group minerals with grain diameters of 100 µm or more and that at the low (<100 ppb) concentrations in these ores, this results in most assays significantly underreporting Pt. This is likely to be true in other low-PGE ores, such that apparent negative Pt anomalies in massive ores may in such cases be attributable to sampling artifacts.

Fluid Inclusion Study of Epithermal Quartz Veins from the Kyaukmyet Prospect, Monywa Copper-Gold Ore Field, Central Myanmar

The Kyaukmyet prospect is located near the main ore bodies of the Kyisintaung and Sabetaung high-sulfidation Cu-Au deposits, Monywa copper-gold ore field, central Myanmar. Lithologic units in the research area are of mainly rhyolite lava, lapilli tuff and silicified sandstone, mudstone and siltstone units of Magyigon Formation which hosted to be polymetallic mineralization. Our field study recorded that epithermal quartz veins are hosted largely in rhyolite lava and lapilli tuff units. Those quartz veins show crustiform, banded (colloform), lattice bladed texture and comb quartz. The main objectives of the present research in which fluid inclusion studies were considered to conduct the nature, characteristics and hydrothermal fluids evolution from the epithermal quartz veins. In this research, there are three main types of fluid inclusions are classified according to their phase relationship (1) two-phase liquid-rich inclusions, (2) the coexisting liquid-rich and vapor-rich inclusions, and (3) only vapor-rich inclusions. Microthermometric measurements of fluid inclusions yielded homogenization temperatures (Th) of 148–282 °C and final ice-melting temperature (Tm) of -0.2°C to -1.4°C . The value of (Tm) are equal to the salinities reaching up 0.35 to 2.07 wt % NaCl equiv. respectively. Estimation formation temperature of the quartz veins provide 190°C and 210°C and paleo-depth of formation are estimated to be between 130m and 210m. Petrography of fluid inclusion and microthermometric data suggest that fluid boiling as well as mixing processes were likely to be happened during the hydrothermal fluid evolution at the Kyaukmyet prospect. According to the characteristics of many parameters including petrography of fluid inclusion, microthermometric data, paleo-depth, evidence of quartz vein textures and types of hydrothermal alteration from the Kyaukmyet prospect allows to interpret these data to be the low-sulfidation epithermal system.

Copper mass flux and evolution of supergene orebody in the Miduk Porphyry Copper Deposit, Iran, and its application to exploration of exotic deposits

The present study used field geology and aimed to model the geological results by modern methods for examining the effects of geological features on the formation of an enriched ore in a mature supergene profile such as Miduk Porphyry Copper Deposit (MPCD). In addition, it aimed to discover which geologic controllers caused the fixation or conduction of Cu in supergene solutions. To this end, the anatomy of the supergene zones was examined by direct sampling and mapping. Analysis of fracture density helps uncover the role of fractures in conveyance of fluids. The results showed that MPCD endured a systematic supergene process, which resulted in the formation of a 200-meter enriched orebody on the top of the hypogene ore. Additionally, the topographic gradient was the most important controller in the migration of supergene solutions to northern side while the north–south trending fractures doubled the lateral flux. Furthermore, the mass balance analysis indicated that 181,000 tons of Cu laterally escaped from the supergene system. Considering the geochemical conditions in sources areas, this amount of metal was sufficient to form a proximal type of exotic mineralization. Further, drainages derived from the main deposit exhibited exotic mineralization, which supported the lateral movement of Cu from the main orebody.

Hydrothermal evolution and mineralization of the Pulang porphyry Cu-Au deposit in the Sanjiang Tethys, Southwest China: Constraints from fluid inclusions and D-O-S isotopes

Pulang is the largest porphyry Cu-Au deposit that formed in the Late Triassic and is located in the eastern Tethys. Its ore-forming fluids and mineral assemblages show some reducing characteristics. Magma and fluid are two key parameters in porphyry mineralization. Studies have shown that syn-mineralization quartz monzonite porphyries have higher oxygen fugacities, which are conducive to mineralization. However, this does not answer the question of why the deposit has reducing characteristics, which should be positively related to fluid activity. Based on detailed geologic observation, hydrothermal evolution and ore-forming process have been divided into three successive periods, namely, pre-mineralization, syn-mineralization (subdivided into three stages, including early-, inter-, and late-mineralization, corresponding to stage 1, 2, and 3 veins), and post-mineralization, in the Pulang deposit. The corresponding fluid inclusions and sulfur isotopic compositions of sulfides are studied on this basis. The results show that the salinity ranges of the stage 1 and stage 2 veins are larger, which indicates that fluid immiscibility may exist. Pyrrhotite is developed in some of the stage 2 veins, and their fluid inclusions contain CH4. However, CH4 was not found in fluid inclusions in veins that do not contain pyrrhotite. The homogenization temperatures and salinities of the fluid inclusions decrease gradually, and the hydrogen and oxygen isotopes gradually approach the meteoric water line overall, from premineralization to postmineralization. Furthermore, sulfur isotopes of pyrrhotite are the highest, indicating a possible additional source of sedimentary sulfur. That is, the ore-forming fluids were dominated by magmatic water, and meteoric water was added in the late stage as the fluid evolved. The trend of the Heishuitang fault is consistent with the extension of the main ore body in the mining area. Because the strata is affected by faults, the strata acts as a good channel for meteoric water. Meteoric water was added to the magmatic fluid after extraction and carried organic matter from the Tumugou Formation and along the cracks. The fluid was mixed, and the ore-forming elements were effectively precipitated in a reducing environment. Therefore, pyrrhotite and CH4 occur in some veins. That may be why the Pulang deposit is giant.

Geochemical and Fe-isotope characteristics of the largest Mesozoic skarn deposit in China: Implications for the mechanism of Fe skarn formation

Skarn deposits are major repositories of Fe and are the principal sources for iron mining in China. However, their mechanism of formation remains debated. Here we investigate the Xishimen (XSM) Fe deposit, located in Wu’an, China. This deposit is a well-known Mesozoic large skarn Fe deposits in the Han-Xing Fe metallogenic belt. Here we report the various features of this Fe deposit that suggest a clear magmatic affinity. We present data on the mineral assemblages, major and trace element data and Fe isotope analysis of magnetite from the XSM Fe deposit. Our results identify four distinct types of magnetite (Type I, II, III and IV). Magnetite type I is characterized by anhedral shape with vesicles in the ores, and is associated with diopside (Di), tremolite (Tr), ±garnet (Gt) and/or augite (Aug), together with phlogopite. Magnetite type I shows high content of TiO2 (0.25–1.21 wt%) and Al2O3 + MnO (0.24–0.72 wt%). These features suggest that magnetite type I is of magmatic origin. Magnetite type IV displays euhedral shape, and is associated with calcite, apatite and pyrite, and is enriched in SiO2, CaO, Sr, Ba, Rb, Nb, and total REE, and depleted in TiO2. These features suggest that magnetite type IV is of hydrothermal origin. The features of magnetite types II and III fall in between magnetite I and magnetite IV. The δ56Fe values are also distinct for the four types of magnetites: δ56Fe is the highest for type I magnetite (average 0.085‰); and the lowest for magnetite type IV (average 0.016‰). Our results also show that the δ56Fe value tends to be higher under high temperature environment and in lower part of the main orebody. Statistical analysis shows a negative correlation between the δ56Fe values and depth.With a view to constrain the origin of the skarn type Fe deposit, we present a conceptual model based on the geochemical and isotope data. We envisage distinct phases during the Fe ore genesis, including: (a) the formation of an iron-rich magma of dioritic composition which reacted with the carbonate wall rocks; (b) the iron-rich magma sinks into the bottom of the magma chamber with high density; (c) volatiles from deep magmatic chamber evolve and interact with the surrounding carbonate rocks; and (d) due to fluid overpressure in the chamber, the iron bearing melt and fluids migrate along structural conduits and precipitate the Fe ore. Because of the difference in temperature, pressure, and oxygen fugacity, the composition of magnetite varied along the fluid/melt conduits. Thus, magnetite type I (high Ti Mt) was mainly distributed in the lower part of the conduit, and magnetite IV (high Si Mt) was mainly concentrated in the upper part during progressive cooling in the conduit. Fe isotope fractionation occurred during the evolution of the Fe-bearing melt/fluid in response to changes in temperature and oxygen fugacity.

Re‐Os Isotopic Age of Molybdenite of the Jingren Deposit and its Mineralogical Significance of Magnetite, Pyrite and Chalcopyrite

AbstractThe Jingren deposit is part of the Qimantage metallogenic belt within the eastern Kunlun orogenic belt, the largest metallogenic belt in Qinghai Province, northwestern China. Exploration data show that the metal resources of the Jingren deposit are greater than 93000 t in a mining area of 76.15 km2, which indicates significant exploration potential in the near future. Three W–E‐trending faults, F1‐3, dominate the extension of the mineralization zone, which consists of chalcopyrite, pyrite, magnetite, galena, sphalerite, and molybdenite as well as bismuth‐bearing minerals. The deposit contains a large amount of late Triassic intrusive rocks, however, previous research did not reach a consensus on the timing or the origin of the mineralization owing to a lack of geochronological data and poor exposure conditions. In the present study, Re‐Os isotopic dating from six molybdenite samples collected from a borehole of the granodiorite in the Jingren deposit using negative thermal ionization mass spectrometry (NTIMS) showed 187Re and 187Os concentrations of 0.26–4.40 ppm and 1.03–16.46 ppb, respectively, with an initial 187Os/188Os value of 0.06 ± 0.19. This proves that the Jingren deposit has a metallogenic age of (225 ± 4) Ma and is the product of united mineralization of the Qimantage metallogenic belt and that the Jingren deposit might actually be an Indosinian metallogeny. In addition, the Re content of these samples, at 0.42 ppm to 7.00 ppm shows that the mineralization was derived mainly from a crustal source. Furthermore, electron probe microanalysis (EPMA) conducted on chalcopyrite obtained from 22 metallic mineral samples revealed (Fe + Cu)/S ratios of 1.801–1.947 with an average of 1.852, which is lower than the ideal value (1.875). Besides, the main ore body formed in a relatively higher temperature environment than the surrounding rocks in the Jingren deposit. These data indicate that the Jingren deposit formed in a metallogenic environment at lower temperature. Moreover, according to the TiO2‐Al2O3‐(MgO + MnO) and TiO2‐Al2O3‐MgO genetic classification diagram for magnetite, the Jingren deposit most likely belongs to the skarn family. In addition, the Co‐Ni‐As genetic classification diagram of the pyrite indicates sedimentary and skarn genetic characteristics.

Primary geochemical haloes and alteration zoning applied to gold exploration in the Zarshuran Carlin-type deposit, northwestern Iran

The Zarshuran gold deposit as sediment-hosted Carlin-type has a total reserve of 120 million metric tonnes and an average grade of 3.5 g/t Au. The dominant hydrothermal alterations associated with gold mineralization are argillic and silicic as well as decalcification of the carbonate host rocks. The exploration geochemistry was applied to characterize the mineralization in the subsurface and peripheries of the open-pit mine at Zarshuran in order to enhance the proved reserves of the gold ores. A sampling network of a 10 × 10 m grid (n = 1720) was applied to almost unweathered surface outcrops to determine the primary geochemical haloes in the study area. Initially, the cut-off grades utilized in the exploratory data analysis were applied to identify the threshold values of the trace elements with lognormal distribution. Then, the central log ratio transformation was used to determine the robustness against outliers to characterize the closure problems with compositional data during Principle Component Analysis (PCA). The supra-ore and near-ore geochemical haloes are recognized by the indicator elements like As-Sb-Hg-Te-Au-Ag-Fe-Mn-Ba-F which are associated with mineral assemblages such as arsenical pyrite, orpiment, realgar, cinnabar, barite, and fluorite. The sub-ore geochemical haloes are characterized by index element association like Cu-Mo-Bi-W-Sn-Co-Ni-V-Cr. The ores at Zarshuran are enriched in Au, As, Sb, Ag, Te, Tl, Zn, Pb, and F but depleted in Cu, W, and Sn, as were observed in many other Carlin-type gold deposits. The enrichment factor of indicator elements (except S, Ag, and Sb) gradually decreases in value from the highly altered and mineralized zones (in proximity of the mine) toward the zones with least alteration and mineralization (in the distal parts of the mine). According to PCA analysis, two main types of ore mineralization occurred at Zarshuran, (1) Au mineralization associated with As, Sb, and Hg, and (2) Cu-Zn-Pb base-metal mineralization related to Ag. The ore-forming index was used to determine the primary axial haloes in both shallow (<−80 m) and deep (>−120 m) levels. The results of this study show that the main ore body may extend eastwardly and downwardly to greater depths, as was verified by the data obtained from diamond drill cores in the eastern part of the mine.

Study on the Genesis of No.II Ore Body in Jia- Ma Orefield

The paper aims to make a comparative analysis on the mineralization and occurrence conditions of two main ore bodies in Jiama deposit in Tibet and speculates that there are close genesis relationship between the No.I and No.Ⅱ ore according to actual exploration and drilling. This paper analyzes their deposit structure and metallogenic fluid structure and draws a conclusion that No.Ⅱ ore is a kind of relatively independent branch ore spatially separated and migrated from No.Ⅰ ore.

Genetic model of carbonatite hosted rare earth elements mineralization from Ambadongar Carbonatite Complex, Deccan Volcanic Province, India

Carbonatites and associated alkaline rocks are the primary sources for REE mineralization. The Ambadongar Carbonatite Complex (ADCC) from NW Deccan Volcanic Province (DVP) constitutes the largest Carbonatite Associated REE Deposits (CARD) in India. ADCC belongs to the final stages of the Late Cretaceous alkaline-carbonatite magmatism associated with main Deccan basalt volcanic activity. The ADCC is an envisioned diatreme structure in which four carbonatitic phases are recognized, mainly calcio-carbonatites and ferro-carbonatites. Each successive carbonatite phase shows higher REE enrichment. The primary REE mineralization with bastnäsite as the dominant REE phase is hosted by pervasive hydrothermally altered ferro-carbonatite plugs. The secondary mineralogy formed with barites in the main orebody during late- to post-magmatic hydrothermal fluid alteration is fluorite, quartz, ankerite, and other REE-bearing minerals like bastnäsite, parisite, synchysite, strontianite, florencite, monazite and columbite.Carbonatite samples contain 18.61% to 52.42% of CaO, and the LOI varies from 5.28% to 38.79%. Most can be classified as calcio-carbonatites. Since all the samples also contain an appreciable amount of Fe2O3 (4.13% to 20.20%) and MnO (0.07% to 5.46%), some may be classified as ferro-carbonatites. Total REE content varies from 0.6 to 4%, with a high Ce concentration and LREE/HREE ratio. The highest values for La, Ce, Pr, and Nd are 1.95%, 1.56%, 0.16%, and 0.45%, respectively.Metasomatism of SCLM from asthenospheric melts followed by the low degree partial melting of the SCLM region is responsible for fertile carbonatite generation in ADCC. The multiphase liquid immiscibility of carbonatite melts from carbonate-silicate magma followed by immiscibility of REE rich carbonatite melt and REE deficient fluoride-rich aqueous fluids explain the higher level of REE enrichment in each successive phases of carbonatites in ADCC.The mineralizing fluids were probably the result of residual magmatic volatiles that brought mainly REE and later SiO2 into the overprinted rocks. Ambadongar carbonatites' stable isotopic compositions agree with a magmatic origin (δ13C = −4.1 ± 1.9‰ [PDB] and δl8O = 10.3 ± 1.7‰ [SMOW]). The C–O stable isotopic modeling indicates re-equilibration under hydrothermal conditions between 180 °C and 70 °C. Significant amounts of REE fluorocarbonate minerals, relatively Sr- and Th-rich, were deposited during re-equilibration. The REE fluorocarbonate bastnäsite-(Ce) occurs as late individual crystals, overgrown on the synchysite and parisite polycrystals. Textural and chemical reactions between the REE fluorocarbonates provide insights into rare-earth elements' mobility during fluid-rock interaction. Early crystallization of synchysite/parisite indicates the high activity of Ca2+, OH−, (SO4)2−, Al and Si in the fluid. Later, the fluid was characterized by increased activity of F−, (SO4)2−, REE and Si, and decreased activity of Ca2+ as reflected in the association of barite, fluorite, quartz, and bastnäsite typical of strongly overprinted ferro-carbonatites.Re-equilibration and recrystallization of the primary minerals in the presence of OH−, (SO4)2−, F−, REE, Al, and Si carried in solution by the hydrothermal fluid is the leading cause behind the refixing of REE in the form of REE fluorocarbonate in REE rich ferro-carbonatites.

Characteristics of Lead and Zinc Polymetallic Deposit and Wall Rock Alteration Zoning in Luziyuan, Yunnan

Luzi Yuan lead and zinc polymetallic deposit is located at Zhenkang anticlinorium which is on the south section of baoshan block. Four main mineralized zones are included in this area, namely I, II, III and V. Among them, II-V1, II-V3 and III-V5 in NO II mineralized zone contain the main orebodies. Througn research the author believes that the deposit shows obvious mineralization alteration zonality from deep to superficial part. It appears that the orebodies are controlled by faulted structure and occur as banded, stratified, stratoid and veined in form along faut fractured zone in the trend of northeast. The analysis and summary of characteristics of mineralization and associated elemengts in this area in this paper provided basis for future prospecting works.

Gold in the Farallones Block of the Shale-Hosted, Clastic-Dominated Castellanos Zinc-Lead Deposit (Northwest Cuba)

The Zn-Pb ores of the Castellanos shale-hosted, clastic-dominated deposit in northwest Cuba average nearly 1 g/t Au, with local maximum concentrations up to 34 g/t Au. This deposit is stratiform with respect to the bedding in the host black shales and shows a bottom to top zoning of ore assemblages made up of a stockwork underlying the main orebody, a basal pyrite-rich zone and a disseminated to massive Zn-Pb ore zone capped by a discontinuous, thin barite-rich zone. Petrographic data and textural relations allow distinguishing five textural types of pyrite (framboidal Py I, colloform Py IIa, euhedral Py IIb, massive Py IIc and banded colloform Py III) successively formed during ore deposition. The main Zn-Pb ore formed after the crystallization of disseminated, sedimentary framboidal pyrite (Py I) in black shales by the superimposition of several crystallization events. The crystallization sequence of the main ore-forming stage evolved from the precipitation of colloform sphalerite and pyrite (Py IIa) with skeletal galena and interstitial dolomite-ankerite to similar ore assemblages but showing subhedral to euhedral crystal habits (Py IIb) and interstitial calcite-rich carbonates. This stage ended with the development of massive pyrite (Py IIc), mainly occurring at the base of the stratiform orebody. A late fracturing stage gave way to the development of a new generation of colloform banded pyrite (Py III) just preceding the crystallization of early barite. Au is mainly concentrated in pyrite showing variable contents in the different textural types of pyrite and a bottom to top enrichment trend. Minimum contents occur in massive pyrite (Py IIc) from the basal pyrite-rich zone (0.18 ppm Au average), increasing in pyrite IIa (from 0.29 to 2.86 ppm Au average) and in euhedral pyrite (Py IIb) (from 0.82 to 9.02 ppm Au average), reaching maxima in colloform banded pyrite (Py III) formed just before the crystallization of early barite at the top of the orebody. Au enrichment in pyrite correlates with that of Sb (0.08–4420 ppm), As (0.7–35,000 ppm), Ag (0.03–1560 ppm) and to a lesser extent Cu (3–25,000 ppm), Ni (0.02–1600 ppm) and Mn (0.6–5030 ppm). Au deposition should have taken place by oxidation and, probably cooling, of reduced (H2S-dominated) fluids buffered by organic matter-rich black shales of the host sedimentary sequence. The input of such reduced fluids in the ore-forming environment most probably occurred alternating with that of the main oxidized fluids which leached Zn and Pb from the large volume of sandstones and siltstones making up the enclosing sequence, thus being responsible for the precipitation of the majority Zn-Pb ore. Supply of Au-carrying reduced fluids might progressively increase over the course of ore formation, reaching a maximum at the beginning of the late fracturing stage. This evolution of Au supply is consistent with the early crystallization of barite since Ba can also only be transported at low temperature by highly reduced fluids. These results highlight the potential of medium-sized, shale-hosted, clastic-dominated deposits to contain economic (by product) Au amounts and show that ore-forming fluids can change from oxidized (SO42+ dominated) to reduced (H2S-dominated), and vice versa, throughout the evolutionary history of a single deposit.