Fluids and Melts at the Magmatic-Hydrothermal Transition, Recorded by Unidirectional Solidification Textures at Saginaw Hill, Arizona, USA

Fluid exsolution and melt evolution at the magmatic-hydrothermal transition are critical processes driving the metal enrichment of porphyry systems. Coeval fluid and melt inclusion assemblages in unidirectional solidification textures (USTs) at Saginaw Hill—a small, porphyry Cu system in southwestern Arizona—record a dynamic and repetitious process of fluid accumulation and release. The cores of quartz crystals throughout the UST bands host coeval silicate melt and brine inclusions but lack vapor-rich inclusions. This could indicate preferential expulsion of vapor and trapping of high-density brine during episodes of fracturing or the direct exsolution of single-phase high-salinity brine from the silicate melt. In contrast, the rims of UST quartz host abundant coeval brine and vapor inclusions, consistent with liquid-vapor immiscibility at lower pressures compared to the corresponding quartz cores. This transition from dominantly coeval silicate melt inclusions and brine in phenocryst cores to coeval brine and vapor in the rims suggests that the Saginaw Hill system underwent cyclic processes of fluid exsolution, accumulation, overpressure, and decompression at relatively stable temperatures (consistently ~650°C) during UST formation. Melt inclusion data indicate that the melt at this stage was highly fractionated and tended toward muscovite saturation. Metal concentrations in the brine were comparable to or higher than those in fluids reported in world-class porphyry Cu systems and were likely the result of both igneous fractionation and the high chloride content of the exsolved fluids. While limited in scale, Saginaw Hill provides evidence for processes that are predicted to occur at the magmatic-hydrothermal transition during the formation of large, well-mineralized porphyry systems

Vein-type gold formation during late extensional collapse of the Eastern Desert, Egypt: the Gidami deposit

Orogenic gold deposits, though construed to focused fluid flow during orogenesis, commonly post-date the main accretionary events. Several lines of evidence indicate that orogenic gold formation in the Arabian–Nubian Shield continued through the orogen collapse stage and associated rapid exhumation and thermal re-equilibration. The Gidami gold deposit in the Eastern Desert of Egypt is associated with post-foliation, brittle-ductile shear zones that deformed a weakly foliated tonalite-trondhjemite massif dated as ~ 704 Ma (U–Pb zircon age). Gold-sulfide quartz veins exhibit textural features indicative of repeated mylonitization, recrystallization, and muscovite crystallization. New $^{40}$Ar/$^{39}$Ar ages of muscovite flakes from the auriferous quartz veins and from the altered wallrock overlap within analytical uncertainty at ~ 583 Ma, which corresponds to the climax of extension-related wrenching and rapid exhumation in the region (~ 596 to 582 Ma). Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) data coupled with microtextural characteristics suggest that early formed pyrite generations experienced substantial fluid-mediated recrystallization, and that a set of metals was remobilized by later fluids. A late generation of fibrous pyrite, ubiquitous in microfractures, deposited while the veins re-opened and deformed. The occurrence of free gold particles along with a late-paragenetic assemblage of galena-sphalerite-chalcopyrite(± hessite ± cervelleite) was related to influx of low salinity, metalliferous H$_{2}$O-NaCl-CO$_{2}$-CH$_{4}$ fluids as indicated by the fluid inclusion laser Raman spectroscopy and microthermometry results. Au-mobilization and redeposition at T ≤ 350 °C and P ~ 1 to 1.7 kbar, triggered by intermittent fluid pluses and thermal re-equilibration, were most likely stimulated by extensional structures and within-plate magmatism. Coincident province- and deposit-scale pressure–temperature-time data highlight the pivotal role of the orogenic collapse tectonics in gold endowment in the Central Eastern Desert’s crust

Polymetallic Sulfide–Quartz Vein System in the Koudiat Aïcha Massive Sulfide Deposit, Jebilet Massif, Morocco: Microanalytical and Fluid Inclusion Approaches

The Koudiat Aïcha Zn-Cu-Pb deposit (3–Mt ore @ 3 wt.% Zn, 1 wt.% Pb, 0.6 wt.% Cu) in the Jebilet massif (Morocco) comprises stratabound lenticular orebodies and crosscutting sulfide-bearing quartz ± carbonate veins in the lower Carboniferous Sarhlef volcano sedimentary succession. The veins are characterized by abundant pyrrhotite, sphalerite, subordinate chalcopyrite and galena and rare Ag and Au minerals. The stratabound massive sulfide ores are attributed to a “VMS” type, whereas the origin of the sulfide–quartz ± carbonate veins remains poorly understood. New mineralogical and microanalytical data (SEM, EPMA and LA-ICP-MS) combined with fluid inclusion results point to two-stage vein formation. The early stage involved C–H–O–N Variscan metamorphic fluids which percolated through fractures and shear zones and deposited pyrite at >400 °C, followed by the formation of pyrrhotite and sphalerite (300 ± 20 °C) in quartz veins and in banded and breccia ores. The pyrrhotite–sphalerite mineralization was overprinted by aqueous brines (34 to 38 wt% eq. NaCl + CaCl2) that precipitated carbonate and Cu-Pb sulfides (±Ag-Au) at ~180–210 °C through mixing with low-salinity fluids during tectonic reworking of early-formed structures and in late extension fractures. The latter ore fluids were similar to widspread post-Variscan evaporitic brines that circulated in the Central Jebilet. Overlapping or successive pulses of different ore fluids, i.e., metamorphic fluids and basinal brines, led to metal enrichment in the quartz–carbonate veins compared to the massive sulfide ores. These results underscore that even a single deposit may record several distinct mineralizing styles, such that the ultimate metal endowment may be cumulative over multiple stages

Basin scale evolution of zebra textures in fault-controlled, hydrothermal dolomite bodies: insights from the Western Canadian Sedimentary Basin

Structurally controlled dolomitization typically involves the interaction of high-pressure (P), high-temperature (T) fluids with the surrounding host rock. Such reactions are often accompanied by cementation and recrystallization, with the resulting hydrothermal dolomite (HTD) bodies including several ‘diagnostic’ rock textures. Zebra textures, associated with boxwork textures and dolomite breccias, are widely considered to reflect these elevated P/T conditions. Although a range of conceptual models have been proposed to explain the genesis of these rock textures, the processes that control their spatial and temporal evolution are still poorly understood. Through the detailed petrographical and geochemical analysis of HTD bodies, hosted in the Middle Cambrian strata in the Western Canadian Sedimentary Basin, this study demonstrates that a single genetic model cannot be applied to all the characteristics of these rock textures. Instead, a wide array of sedimentological, tectonic and metasomatic processes contribute to their formation; each of which is spatially and temporally variable at the basin scale. Distal to the fluid source, dolomitization is largely stratabound, comprising replacement dolomite, bedding-parallel zebra textures and rare dolomite breccias (non-stratabound, located only proximal to faults). Dolomitization is increasingly non-stratabound with proximity to the fluid source, comprising bedding-inclined zebra textures, boxwork textures and dolomite breccias that have been affected by recrystallization. Petrographical and geochemical evidence suggests that these rock textures were initiated due to dilatational fracturing, brecciation and precipitation of saddle dolomite as a cement, but significant recrystallization occurred during the later stages of dolomitization. These rock textures are closely associated with faults and carbonate-hosted ore deposits (e.g. magnesite, rare earth element and Mississippi Valley–type mineralization), thus providing invaluable information regarding fluid flux and carbonate metasomatism under elevated P/T conditions

Alichur Dome, South Pamir, Western India-Asia Collisional Zone: Detailing the Neogene Shakhdara-Alichur Syn-collisional Gneiss-Dome Complex and Connection to Lithospheric Processes

Neogene, syn‐collisional extensional exhumation of Asian lower–middle crust produced the Shakhdara–Alichur gneiss‐dome complex in the South Pamir. The <1 km‐thick, mylonitic–brittle, top‐NNE, normal‐sense Alichur shear zone (ASZ) bounds the 125 × 25 km Alichur dome to the north. The Shakhdara dome is bounded by the <4 km‐thick, mylonitic–brittle, top‐SSE South Pamir normal‐sense shear zone (SPSZ) to the south, and the dextral Gunt wrench zone to its north. The Alichur dome comprises Cretaceous granitoids/gneisses cut by early Miocene leucogranites; its hanging wall contains non/weakly metamorphosed rocks. The 22–17 Ma Alichur‐dome‐injection‐complex leucogranites transition from foliation‐parallel, centimeter‐ to meter‐thick sheets within the ASZ into discordant intrusions that may comprise half the volume of the dome core. Secondary fluid inclusions in mylonites and mylonitization‐temperature constraints suggest Alichur‐dome exhumation from 10–15 km depth. Thermochronologic dates bracket footwall cooling between ~410–130 °C from ~16–4 Ma; tectonic cooling/exhumation rates (~42 °C/Myr, ~1.1 km/Myr) contrast with erosion‐dominated rates in the hanging wall (~2 °C/Myr, <0.1 km/Myr). Dome‐scale boudinage, oblique divergence of the ASZ and SPSZ hanging walls, and dextral wrenching reflect minor approximately E–W material flow out of the orogen. We attribute broadly southward younging extensional exhumation across the central South Pamir between ~20–4 Ma to: (i) Mostly northward, foreland‐directed flow of hot crust into a cold foreland during the growth of the Pamir orocline; and (ii) Contrasting effects of basal shear related to underthrusting Indian lithosphere, enhancing extension in the underthrust South Pamir and inhibiting extension in the non‐underthrust Central Pamir

Germline variation at 8q24 and prostate cancer risk in men of European ancestry

Chromosome 8q24 is a susceptibility locus for multiple cancers, including prostate cancer. Here we combine genetic data across the 8q24 susceptibility region from 71,535 prostate cancer cases and 52,935 controls of European ancestry to define the overall contribution of germline variation at 8q24 to prostate cancer risk. We identify 12 independent risk signals for prostate cancer (p < 4.28 × 10−15), including three risk variants that have yet to be reported. From a polygenic risk score (PRS) model, derived to assess the cumulative effect of risk variants at 8q24, men in the top 1% of the PRS have a 4-fold (95%CI = 3.62–4.40) greater risk compared to the population average. These 12 variants account for ~25% of what can be currently explained of the familial risk of prostate cancer by known genetic risk factors. These findings highlight the overwhelming contribution of germline variation at 8q24 on prostate cancer risk which has implications for population risk stratification

Trans-ancestry genome-wide association meta-analysis of prostate cancer identifies new susceptibility loci and informs genetic risk prediction.

Prostate cancer is a highly heritable disease with large disparities in incidence rates across ancestry populations. We conducted a multiancestry meta-analysis of prostate cancer genome-wide association studies (107,247 cases and 127,006 controls) and identified 86 new genetic risk variants independently associated with prostate cancer risk, bringing the total to 269 known risk variants. The top genetic risk score (GRS) decile was associated with odds ratios that ranged from 5.06 (95% confidence interval (CI), 4.84-5.29) for men of European ancestry to 3.74 (95% CI, 3.36-4.17) for men of African ancestry. Men of African ancestry were estimated to have a mean GRS that was 2.18-times higher (95% CI, 2.14-2.22), and men of East Asian ancestry 0.73-times lower (95% CI, 0.71-0.76), than men of European ancestry. These findings support the role of germline variation contributing to population differences in prostate cancer risk, with the GRS offering an approach for personalized risk prediction

Fine-mapping of prostate cancer susceptibility loci in a large meta-analysis identifies candidate causal variants

Prostate cancer is a polygenic disease with a large heritable component. A number of common, low-penetrance prostate cancer risk loci have been identified through GWAS. Here we apply the Bayesian multivariate variable selection algorithm JAM to fine-map 84 prostate cancer susceptibility loci, using summary data from a large European ancestry meta-analysis. We observe evidence for multiple independent signals at 12 regions and 99 risk signals overall. Only 15 original GWAS tag SNPs remain among the catalogue of candidate variants identified; the remainder are replaced by more likely candidates. Biological annotation of our credible set of variants indicates significant enrichment within promoter and enhancer elements, and transcription factor-binding sites, including AR, ERG and FOXA1. In 40 regions at least one variant is colocalised with an eQTL in prostate cancer tissue. The refined set of candidate variants substantially increase the proportion of familial relative risk explained by these known susceptibility regions, which highlights the importance of fine-mapping studies and has implications for clinical risk profiling. © 2018 The Author(s).Prostate cancer is a polygenic disease with a large heritable component. A number of common, low-penetrance prostate cancer risk loci have been identified through GWAS. Here we apply the Bayesian multivariate variable selection algorithm JAM to fine-map 84 prostate cancer susceptibility loci, using summary data from a large European ancestry meta-analysis. We observe evidence for multiple independent signals at 12 regions and 99 risk signals overall. Only 15 original GWAS tag SNPs remain among the catalogue of candidate variants identified; the remainder are replaced by more likely candidates. Biological annotation of our credible set of variants indicates significant enrichment within promoter and enhancer elements, and transcription factor-binding sites, including AR, ERG and FOXA1. In 40 regions at least one variant is colocalised with an eQTL in prostate cancer tissue. The refined set of candidate variants substantially increase the proportion of familial relative risk explained by these known susceptibility regions, which highlights the importance of fine-mapping studies and has implications for clinical risk profiling. © 2018 The Author(s).Peer reviewe