Geology and pyrite-polymetallic mineralization of the forecasted Limonite deposit, Rassokhinsky ore cluster (Yenisei ridge)

The development of Russia’s largest Gorevskoye leadzinc deposit (Gorevsky GOK, Novoangarsky OK) will depend on promising deposits of the Angara polymetallic ore region, in particular, those of the Rassokhinsky ore cluster. Based on the analysis of geological and geophysical information of previous and current studies, a major Limonite pyrite-polymetallic (massive sulfide) deposit is forecasted within it. The main lithological and stratigraphic criterion for the localization of ores is determined by their confinement to high-carbon black quartz-sericite schists of the upper subformation of the Potoskuy suite of the Upper Riphean. In the top of this pack, layered and massive pyrite-polymetallic ores, 70– 140 m thick, are localized. Based on PPA data, lead and zinc content in core varies from fractions of a percent to several percent, based on the ICP-AES method: 0,1– 3,7 % Pb, 0,1–6,4 % Zn, Pb : Zn ratio is 1 : (1–10).

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

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.

Geodynamic conditions of massive sulfide formation in the Magnitogorsk megazone

Research subject. Volcanism, rock geochemistry, geodynamics, and massive sulfide formation in the Magnitogorsk megazone (MMZ) of the Southern Urals in the Middle Paleozoic.Materials and Methods. Across the largest part of the massive sulfide deposits under investigation, the authors conducted route studies, including geological surveys of individual ore fields and quarries of deposits, core samples of deep wells and transparent sections. Representative analyses of petrogenic and microelements were performed using wet chemistry and ICP-MS in analytical centers in Russia and Europe. Along with the authors’ data, analytical materials published by Russian and foreign researchers were used. Geodynamic reconstructions were carried out taking into account regional data on gravics, thermal field, magnetometry, and seismic stu dies, including «Urseis-95».Results. The geodynamic reconstructions established that the main elements of the paleostructure of the Southern Urals in the Devonian were the subduction zone of the eastern dip and asthenospheric diapirs that penetrated into the «slab-window», which determined the type of volcanic belts, the composition and volume of volcanic rocks of pyrite-bearing complexes, and ore matter of pyrite deposits. The following geodynamic zones in the MMZ were identified: 1 – polychronous accretion prism; 2 – frontal and developed island arcs (D1e2–D2ef1); 3 – zone of back-arc spreading (D1e2); 4 – rear island arc (D2ef1).Conclusions. All investigated zones and ore areas are characterized by an autonomous development of volcanism, a special deep structure and a different composition, as well as by a different volume of massive sulfide deposits that vary in the Cu and Zn ratios and Pb, Ba, Au amounts. In the MMZ volcanic complexes, three groups of plume source basalts are distinguished. The results can be used in predictive-estimation and search operations for massive sulfide mineralization.

Mineral formation conditions in acid magmatic systems related to the formation of massive sulfide deposits of the Urals and Altai-Sayany area

Studies of melt inclusions in quartz indicate the similarity of acid magmatic systems of massive sulfde deposits in the Urals and Altai-Sayany region. The melts of normal alkalinity corresponding to rhyodacite and rhyolite compositions and related to the tholeiitic series are dominant in all the deposits considered. The magmas are characterized by the same type evolution with a decreasing content of main oxides (TiO2, Al2O3, FeO, MgO, CaO, Na2O, K2O) and an increasing SiO2 content. Our results show the accumulation of Cu in relatively low-H2O acidic melts of ancient (Cambrian) deposits of the Altai-Sayany region and low metal contents in the intermediate (Silurian–Devonian) and H2O-saturated magmas of the Urals. The youngest (Devonian) magmas of Siberia evolve simultaneously along these two directions. The analysis of melt inclusions in quartz suggests that the minimum contents of trace and rare earth elements are characteristic of the Silurian-Devonian acid melts of the Urals, with their maximum contents in the youngest (Devonian) magmas and the intermediate contents of ancient (Cambrian) magmatic systems of the Altai-Sayany region. The features of rare and rare earth element patterns in melt inclusions in quartz indicate the similarity of acid magmatic systems of massive sulfde deposits in the Urals and Altai-Sayany region with present-day suprasubduction melts in the ocean-continent transition zones. Computational modeling using data on melt inclusions in quartz confrms our previous conclusions (Simonov, Maslennikov, 2020) that the occurrence of contrasting (basic and felsic) volcanic complexes with massive sulfde deposits in the Urals and Altai-Sayany region is a result of evolution of basaltoid magmas. Keywords: conditions of mineral crystallization, basaltic-rhyolitic complexes, massive sulfde deposits, melt inclusions, quartz, acidic melts.

Detachment-parallel recharge explains high discharge fluxes at the TAG hydrothermal field

Submarine massive sulfide deposits on slow-spreading ridges are larger and longer-lived than deposits at fast-spreading ridges1,2, likely due to more pronounced tectonic faulting creating stable preferential fluid pathways3,4. The TAG hydrothermal mound at 26°N on the Mid-Atlantic Ridge (MAR) is a typical example located on the hanging wall of a detachment fault5-7. It has formed through distinct phases of high-temperature fluid discharge lasting 10s to 100s of years throughout at least the last 50,000 years8 and is one of the largest sulfide accumulations on the MAR. Yet, the mechanisms that control the episodic behavior, keep the fluid pathways intact, and sustain the observed high heat fluxes of up to 1800 MW9 remain poorly understood. Previous concepts involved long-distance channelized high-temperature fluid upflow along the detachment5,10 but that circulation mode is thermodynamically unfavorable11 and incompatible with TAG's high discharge fluxes. Here, based on the joint interpretation of hydrothermal flow observations and 3-D flow modeling, we show that the TAG system can be explained by episodic magmatic intrusions into the footwall of a highly permeable detachment surface. These intrusions drive episodes of hydrothermal activity with sub-vertical discharge and recharge along the detachment. This revised flow regime reconciles problematic aspects of previously inferred circulation patterns and can be used as guidance to one critical combination of parameters that can generate substantive mineral systems.

On genesis of massive sulfide polymetallic ore deposits of Rudny Altai

Many geologists assign most of large- and medium-sized massive sulfide polymetallic ore deposits of Eastern Kazakhstan to the VMS type. These ore deposits formed in the Devonian, under conditions of rifting and active basalt-andesite-rhyolite volcanism. Ore bodies of these deposits are noted to be clearly confined to formations of several geochronologic levels (D1e to D3fm). Hydrothermal-sedimentary syngenetic and hydrothermal-metasomatic ores are distinguished. High concentrations of base metals in the ores (above 10 % sum metals) and their rather simple mineral composition (chalcopyrite, pyrite, galena, and sphalerite) are a characteristic feature of all the massive sulfide polymetallic ore deposits of Rudny Altai. The ores are noted to be multicomponental, with elevated contents of the admixtures of precious metals and rare elements (Cd, Se, Bi, Te, Ta, W, etc.). Mineralogical investigations of the ores have demonstrated an intricate relationships of the major ore minerals (chalcopyrite, pyrite, sphalerite, galena) that exhibit several generations and different geochemical specialization. Minerals of Au, Ag, Te, Bi, and other elements are encountered as individual grains or microscopic inclusions and stringers in minerals of Cu, Pb, and Zn. A significant vertical range of the ore mineralization (more than 100 m), the complexity and long duration of the ore-forming processes, the clearly defined confinement of the ore mineralization to certain geochronologic levels, – all these allow us to suppose a possibility of discovery of new ore lodes or individual ore deposits within the already known ore fields of the Kazakhstan segment of Rudny Altai

The Ecological Impacts of Mining at Seafloor Massive Sulfide Deposits on Megafaunal Assemblage Structure and Population Connectivity

<p>Deep-sea mining is rapidly becoming a reality, yet there are considerable gaps in our knowledge of the seabed assemblages that could be affected by mining activities. Seafloor Massive Sulfide (SMS) mining is expected to remove nearly all organisms in the immediate area and alter the remaining habitat, so that mitigation strategies for SMS mining will most likely need to include the establishment of protected areas to preserve the biodiversity that is lost at mine sites. Prospecting licences have been issued previously for SMS deposits within the New Zealand Exclusive Economic Zone (EEZ), however little is known about the seabed assemblages potentially at risk from SMS mining, particularly with respect to their structure (at multiple spatial scales) and the connectivity of assemblages at different sites. Designing studies to provide this information can be aided by turning to terrestrial, freshwater and shallow marine systems, where the fields of ecological theory, environmental management and conservation theory are better developed (Chapter 1). Prior to detailed investigations into the assemblage structure and population connectivity of New Zealand SMS deposits, it is essential to understand the global context of SMS mining. This was undertaken through an extensive literature review of SMS deposits, including their geology, seafloor communities, impacts from mining, international and national regulation, and environmental management (Chapter 2). In order to investigate the large-scale spatial distribution and structure of seafloor assemblages at SMS deposits, three New Zealand seamounts previously licenced for the prospecting phase of SMS mining were surveyed. Video footage from a towed camera was analysed to identify and characterise assemblages, and their association with environmental variation was investigated. Analysis of 249 video samples (each 250 m in length) distributed amongst the three seamounts indicated that SMS deposits support unique assemblages and that there were strong links between assemblage structure and environmental variation at a range of spatial scales. There was also a complex distribution of assemblages amongst the seamounts, suggesting a network of protected areas would be the most effective method for spatial management. Such networks should include sites that support the unique assemblages found in association with SMS deposits (Chapter 3). The fine-scale distribution and structure of assemblages at SMS deposits was investigated by using data from a single SMS deposit, Proteus 1, and comparing it to a Reference Site selected to have similar size and seabed characteristics to the deposit. Video footage from a Remotely Operated Vehicle (ROV) was used to identify and characterise assemblages, and their association with environmental conditions. Analysis of 153 video samples (each 15 m in length) confirmed the existence of assemblages unique to SMS deposits, and indicated that environmental characteristics specific to the deposit are responsible for the observed patterns of faunal distribution. Although five assemblages were shared between Proteus 1 and the Reference Site, six assemblages were unique to Proteus 1. This suggested that the proposed Reference Site would be inadequate on its own in terms of protecting the biological diversity present at the mine site but could contribute to a network of protected areas (Chapter 4). The issue of connectivity was addressed by examining the genetic connectivity of populations of the endemic hydrothermal vent mussel, Gigantidas gladius. Universal markers, archived material and off-the-shelf DNA extraction kits were used to investigate a cost effective approach. The assessment utilised variation in 586 base pairs of the mitochondrial cytochrome oxidase I subunit (COI) from 150 individuals in seven populations of G. gladius. Small sample sizes limited the recommendations that could be made for environmental management; however interpretation of the available sequences indicated panmixia with limited genetic structure and high connectivity amongst populations. Central Kermadec Volcanic Arc populations had particularly high haplotypic diversity and migrant exchange, suggesting they could be important for maintaining regional genetic connectivity and would merit inclusion in seabed protection measures (Chapter 5). Establishing protected areas for biodiversity needs to utilise all of the available information. The integrated findings of this thesis highlight the need for a network of protected seabed areas along the Kermadec Volcanic Arc to help mitigate the impacts of any future SMS mining activities. These networks should be highly connected (as determined by genetic connectivity) and include both active and inactive SMS areas to conserve 1) the endemic vent fauna in active areas and 2) the unique assemblages found in both environments (Chapter 6).</p>