Mineralium Deposita最新文献

Epithermal precious metal deposits are uncommon within the Archean rock record, as are detailed descriptions of their associated features and modes of formation. The Vent prospect is a Neoarchean Au–Ag occurrence within the Eastern Wabigoon Subprovince of the Superior Province in Ontario. It is hosted by aphyric, and quartz ± feldspar-porphyritic aphanitic dacitic flows that show remnants of spine-like structures within blocky flow top breccia facies that lack visible hyaloclastite, consistent with subaerial emplacement. Numerous phreatic breccia dikes containing rounded, heterolithic, fragments in a fine rock flour and locally altered matrix intrude the dacitic host rocks, supporting a subaerial setting. Discordant replacement and stringer Au- and Ag-bearing pyrite mineralization is associated with a decimeter-scale, zoned, discordant sequence of metamorphic associations consisting of a) quartz-pyrite; b) kyanite-quartz; c) muscovite-kyanite; and d) muscovite. The geochemical characteristics of these metamorphic associations reflect intense pre-metamorphic acidic alteration. These lithofacies, alteration characteristics, and mineralization styles are consistent with a subaerial volcanic edifice altered by acidic hydrothermal fluids, which periodically brecciated the edifice. We propose that the features that characterize the Vent prospect are consistent with those of Phanerozoic epithermal systems. New U–Pb zircon geochronology of the host dacites indicate formation at ca. 2720 Ma, suggesting that the Vent prospect may represent one of the oldest identified epithermal deposits preserved in the ancient rock record. The recognition of epithermal mineralization in Archean greenstone belts underlain by Mesoarchean crust, such as those of the Eastern Wabigoon, opens up the possibility of potential for gold and silver in other underexplored Archean greenstone belts.

We provide timestamps for the major zinc-lead (Zn-Pb) Mississippi Valley-type Black Angel deposit (Greenland) based on new pyrite rhenium-osmium (Re-Os) isotope geochemistry data: (1) a Re-Os isochron age 1,884 ± 35 million years ago (Ma – 2σ, 1.8%) for subhedral pyrite cemented by sphalerite ± galena in dolomitized clean limestone, and, (2) a Re-Os model age 1,828 ± 16 Ma (2σ, 0.9%) for epigenetic massive pyrite in siltstone/mudstone cap rock. Zinc-lead mineralization in evaporite-bearing carbonates in the Karrat Basin took place ca. 1,884 Ma at the time of far-field fluid flow associated with back-arc spreading ca. 1,900–1,850 Ma. Mineralization predates the development of the Rinkian foreland basin (ca. 1,850 – < 1,800 Ma) and a collisional stage (ca. 1,830 – < 1,800 Ma) in the context of the telescoping Rinkian and the Nagssugtoqidian Orogens. Replacement of clean carbonate and sustained acid neutralization led to significant sphalerite precipitation ca. 1,884 Ma. Conversely, precipitation of epigenetic massive pyrite in the cap rock ca. 1,828 Ma may signal (1) the lack of chemical reactivity of the cap rock for the pH-buffered conditions needed for Zn-Pb mineralization, and (2) the unfavorable impact of incipient regional Rinkian metamorphism (ca. 1,830–1,800 Ma) and tectonic compression on aquifer permeability and continued brine migration. The initial ¹⁸⁷Os/¹⁸⁸Os ratio (Os_i-pyrite = 1.07 ± 0.32) from isochron regression identifies a crustal origin for Os and, by corollary, other metals in the ca. 1,884 Ma Zn-Pb mineralization. Although the Rae Craton basement rocks comprise the dominant source for metals (based on our Os_i-pyrite and δ⁶⁶Zn_{pyrite/sphalerite} data), we identify a complementary contribution in Zn (maximum 12–24%) from Paleoproterozoic sedimentary carbonate. This source of Zn in sedimentary calcite is deemed possible in the context of Paleoproterozoic seawater at high Na/Cl ratio and in the absence of Zn-based eukaryotic metabolism in shallow marine environment.

Tungsten enrichment during the formation of giant W deposits is thought to be related to magmatic and hydrothermal processes. However, the mechanisms of W enrichment and their role in controlling ore formation remain unclear. Zircon is a ubiquitous accessory mineral that can provide a record of the physicochemical conditions during mineralization. Dahutang in South China is a giant W deposit (1.89 Mt WO₃ at 0.18%) associated with the late Mesozoic granites. In this study, we report new zircon morphological, geochronological, and chemical data for the most evolved Li-mica albite granite in the Dahutang deposit, in order to determine the processes of W enrichment. We classified the zircons into three types based on their appearance and composition. Type-IA and -IB zircons (ca. 145 Ma) successively crystallized from metasedimentary-derived magmas (δ¹⁸O = 8.9 ± 0.3‰) at 786–732 °C. Type-II zircons formed by interaction between volatile-rich melts and Type-I zircons at 669 ± 39 °C. Type-III zircons formed by autometasomatism of earlier Type-I and -II zircons, which involved exsolved hydrosilicate fluids. Our numerical model shows that the granitic melts have undergone > 95% fractional crystallization and experienced metasomatism by hydrosilicate fluids, during which the rare-metals (W, Nb, and Ta) were extensively enriched. Furthermore, we compiled data for ten W deposits across South China to investigate the key factors controlling the formation of giant W deposits. The strong correlation (R² = 0.79) between WO₃ tonnage and zircon Hf content indicates that an extensive and multi-stage evolution may be the key factor controlling the formation of giant W deposits.

Porphyry deposits of the Cu-Mo-Au-Re metal spectrum mainly occur in arc settings, but only some segments of the same arc host significant metal resources. The factors controlling the variable metal endowment in magmatic arcs remain unclear. Here, we conducted zircon U-Pb age, trace element, and Hg isotope studies on the ore-bearing (i.e., fertile) and coeval barren granitic rocks from the Upper Triassic Yidun arc, eastern Tibetan Plateau. The results show that the barren granites from the northern Yidun arc display normal arc magma features, and have low oxygen fugacities (ΔFMQ= -3.7 to -0.5), low water contents. Their negative Δ¹⁹⁹Hg values (-0.20 to 0.02‰) indicate that they were mainly derived from continental basement rocks. The fertile granites from the southern Yidun arc exhibit adakitic geochemical affinity (i.e., high Sr/Y and La/Yb ratios), high oxygen fugacities (ΔFMQ = 0.2 to 2.7), and high water contents. Their positive Δ¹⁹⁹Hg values (-0.07 to 0.23‰) indicate an oceanic source of the Hg and suggest that they were derived from an enriched mantle source modified by oxidizing, subduction-related fluids/melts. The contrasting characteristics of fertile and barren granites indicate that magma sources likely have a critical control on the metallogenic potential of arc magmas, with slab-derived fluids imprinting high fO₂ and volatile contents for the formation of productive intrusions in arc settings. Arc magmas derived from oxidized and water-riched magma sources have a predisposition to form porphyry Cu deposits, and should be regarded as priority targets for porphyry deposit exploration.

The El Zorro gold district is the most recent gold discovery in the Coastal Cordillera of northern Chile. Ternera is the largest deposit in the district with total resources currently estimated at 1.282 Moz. New geology, geochemistry and geochronology data indicate that hydrothermal mineralization is mostly hosted within felsic to intermediate, ilmenite-bearing calc-alkaline dikes and stocks of the Upper Triassic to Lower Jurassic Relincho Pluton, and some of the adjacent Devonian to Carboniferous metasediments of the Chañaral Epimetamorphic Complex. Sheeted veins, veinlets, and fault zones with quartz, low amounts of pyrite, pyrrhotite and arsenopyrite, and local calcite are surrounded by narrow haloes of albite-biotite-quartz ± sulfides-K-feldspar-sericite-chlorite. Gold (mostly in the veins) is associated with elevated W-Bi and also As-Te-Sn, and not with iron enrichment or base metals, even though this system is proximal (~ 20 km) to IOCG and IOA deposits of the Coastal Cordillera. The main phase of gold mineralization occurred soon after emplacement of tonalitic dikes and granodiorite from the Relincho and Cuevitas plutons (U–Pb zircon between ~ 205 and 190 Ma), about 80 m.y. later than the development of orogenic fabrics. An absolute upper age limit is provided by compositionally distinct ore-cutting mafic dikes dated at 175–170 Ma (U–Pb apatite). The deposit falls into the intrusion-related gold category, as indicated by the cutting of earlier orogenic fabrics, the metal and alteration associations, and the spatial and temporal connection to reduced ilmenite-series intrusions, which are also very similar geochemically to the ‘type-locality’ IRG intrusions of the Tintina Belt in Yukon/Alaska. The El Zorro gold district represents the oldest and geologically western-most mineralizing event in the Central Andes of northern Chile, consistent with its time–space placement within the tectonic framework of easterly-younging mineralization and igneous activity in the Chilean Cordillera.

The formation of volatile-rich phases in magmatic sulfide systems has been interpreted at least in six different ways. The most popular model attributes their origin to secondary processes, mostly due to the presence of serpentine, chlorite, phlogopite, amphibole, and calcite. While chlorite and serpentine are likely to form as alteration products, the other volatile-rich minerals have the potential to originate in a range of ways, including by primary magmatic processes. Based on mineralogical and petrological studies, it was recently suggested that volatile- and incompatible element-rich halos around sulfide globules may form due to the interaction between three immiscible liquids: silicate, carbonate, and sulfide. This hypothesis was confirmed by experimental data revealing the systematic envelopment of sulfide globules by carbonate melt, indicating their mutual affinity. In this study, we present data on isotopic signatures and trace element distributions of three minerals commonly found in spatial association with sulfides—calcite, apatite, and zircon—to address the question of the source and nature of volatiles and other incompatible elements involved in the formation of the halos. Here we compare our new hypothesis with all the previously proposed explanations to show if they can be consistent with obtained results. Our findings indicate that both mantle and crustal sources play a role in the formation of volatile- and incompatible element-rich halos, strongly correlating with sulfur isotope data previously reported for the sulfide globules in the same intrusions. This correlation confirms the shared origin of sulfides, carbonate and fluids during ore-forming processes, ruling out the secondary origin of volatile-rich phases. The isotope and trace element signatures support the newly proposed hypothesis that volatile- and incompatible element-rich halos could have been formed due to the interaction of immiscible sulfide, carbonate, and silicate melts. The volatile-rich carbonate melt could be sourced from the mantle or it could be added from the crust. Regardless of the origin, carbonate melt and sulfide liquid both immiscible with mafic magma tend to stick to each other resulting in the formation of volatile- and incompatible element-rich halos commonly documented in magmatic sulfide deposits.

The invisible-gold deposits known as Carlin-type are becoming more important as easier to find deposits are progressively depleted. The combination of the invisible nature of the Au in these deposits, as well as the limited surface indicators of these deposits, makes exploration to find new Carlin-type deposits extremely difficult. Comprehensive mineralization models are essential to find new Carlin-type deposits in similar geologic settings. The Nadaleen Trend of Yukon, Canada, is one such district where an improved understanding of this deposit type has led to new discoveries. Previous studies compared and contrasted the tectonic setting, host rock depositional setting, structural preparation, and mineralization style of the Nadaleen Trend with those in Carlin-type localities, Nevada. However, the comparisons at an atomic scale, between Carlin-type Au deposits in the Nadaleen Trend and those in Nevada, has yet to be investigated. This study fills this knowledge gap by combining high resolution microanalytical techniques with atom probe tomography to examine the distribution of Au and other trace elements in the Nadaleen Trend, compare them to a representative Carlin-type deposit in Nevada (Turquoise Ridge), and determine how widespread the mineralization model is. Our findings show that in the Nadaleen Trend, as in Nevada, Au is generally directly linked with As at the macro to atomic scale, and is incorporated into As/Au rich overgrowths on sedimentary/diagenetic pyrite. Gold-rich pyrite rims in the Nadaleen Trend are generally smaller than those found in Nevada (0.5–2 µm vs > 10 µm), although the ore grades appear comparable. We find that the Au in the pyrite of the Nadaleen Trend is homogenously distributed (i.e. lattice bound) at the atomic scale, but that there is a notable enrichment of As surrounding individual Au atoms. These findings are in agreement with those from previous work on a representative deposit in Nevada, and support the assertation that As is the key ingredient in facilitating the incorporation of Au into the pyrite lattice. Arsenic as an essential component in the trapping mechanisms of Au in CTG deposits, is something that has been as to yet underappreciated in the current models of CTG deposit formation.

Gold mineralization in hydrothermal systems at slow- to ultraslow-spreading ridges commonly occurs either in the hangingwall or the footwall of the detachment fault. However, the Tianxiu Vent Field (TVF) on Carlsberg Ridge is, to our knowledge, the only known example where the mineralization occurs directly at the termination zone of a detachment fault. Located approximately 5 km south of the rift axis near 3°48′N on the slow-spreading Carlsberg Ridge, TVF provides a unique opportunity for studying gold mineralization in this context. Detailed analyses of the mineralogy, mineral chemistry, and bulk geochemistry of massive sulfides from Tianxiu reveal several key findings: (1) both visible gold (native gold and electrum) and invisible gold are predominantly hosted in Cu-rich minerals such as isocubanite and covellite; (2) the content of Au (mean = 5.72 ± 4.38 ppm, n = 43) is positively correlated with Co, Cu, Bi, and Se; and (3) the gold mineralization occurs primarily at high-temperatures under strongly reducing conditions, with additional gold mineralization during late-stage silicification and seafloor weathering. When compared to other detachment-fault-associated deposits along slow- to ultraslow-spreading ridges, the ultramafic source rocks and the strongly reducing conditions at TVF appear to have facilitated Au mineralization. Additionally, the intensity of the fluid/rock interaction is possibly an important factor controlling the distribution of gold. The heterogeneous distribution of gold in Tianxiu is likely due to the spatial variability of fluid pathways within a highly permeable termination zone of the detachment fault. This study underscores a unique mineralization model of gold at the termination of a detachment fault on slow-spreading ridges, which has significant implications for the exploration of massive sulfide resource in off-axis regions.