Mineralium Deposita最新文献

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.

Precambrian iron oxide copper-gold (IOCG) systems have commonly experienced multiple mineralising and tectonothermal events and identifying their timing and geodynamic framework is challenging. World-class IOCG deposits in the Olympic Cu-Au Province, South Australia, are dominated by hematite and formed in the upper crust, while the magnetite-dominated Cu deposits hosted in granulite facies rocks are considered to represent the deeper expression of giant IOCG system. However, the application of novel in-situ Lu-Hf apatite geochronology reveals the magnetite-hosted Cu mineralisation is significantly younger and unrelated to the well-known ~ 1590 Ma Gawler Craton IOCG systems. Apatite Lu-Hf ages from the granulite that predates Cu mineralisation give ages of 1490 Ma. Infiltration of Cu-bearing fluids resulted in recrystallisation of apatite, LREE mobilisation and formation of secondary monazite. Lu-Hf ages for syn-mineralisation apatite give 1460 Ma, consistent with c. 1460 Ma U-Pb ages from secondary monazite. In contrast to the apatite in situ Lu-Hf ages, all apatite types produce a single U-Pb age of c. 1460 Ma, demonstrating the ability of Lu-Hf to preserve a more complete history of apatite formation than U-Pb in high- to medium-temperature rock systems. The timing of mineralisation coincides with the onset of Nuna fragmentation, representing a previously unrecognised driver for mineral system formation in southern Australia that installed Cu in crust previously dehydrated during a long history of granulite-grade tectonic events. The recognition of this Cu system in rocks generally considered unprospective shows that continental breakup can rejuvenate metallic systems in otherwise unprospective crust.

Stratiform sediment-hosted Cu deposits are significant global sources of Cu and other important metals. The Polish Kupferschiefer produces Ag, Au, Pb, Ni, Se, and Re as by-products, whereas Co is one the of most important metals in the stratiform sediment-hosted Cu-Co deposits of the Central African Copperbelt and the Namibian Dolostone Ore Formation deposit. This study combines new and published laser ablation inductively coupled plasma mass spectrometry sulfide trace element data from these stratiform sediment-hosted copper districts. All the investigated districts exhibit sulfides occurring as disseminations and within later veins. Chalcopyrite, sphalerite, and pyrite trace element contents vary significantly between the metallogenic districts as well as between different ore stages. Random Forest discriminates the stratiform sediment-hosted Cu(-Co) districts based on trace element geochemistry. High Ag and Tl in chalcopyrite is attributed to the Polish Kupferschiefer, Ga and Ge to the Katanga Copperbelt, and Zn and In to the Dolostone Ore Formation deposit. Sphalerite from the Polish Kupferschiefer and the Dolostone Ore Formation deposit can be distinguished on the basis of the Fe and Cd contents. Cobalt and As are significantly elevated in pyrite from the Katanga Copperbelt and Mn in pyrite from the Dolostone Ore Formation deposit. The trace element contents also show that the stratiform sediment-hosted Cu(-Co) deposit sulfide data cluster separately from other deposit types. The variation in sulfide trace element contents between the three investigated stratiform sediment-hosted Cu(-Co) districts suggests that sulfide chemistry is related to the geology of the host basin and the nature of the underlying basement, which includes preexisting ore occurrences.

In the Voisey’s Bay complex, sulfide-matrix breccias developed through the percolation of dense sulfide melt, leading to the displacement of the silicate melt within partially molten silicate-matrix breccias. In these sulfide matrix-breccias, hydrous silicate rims are commonly present at the interface between the sulfide matrix and the silicate framework. Multiple lines of evidence support a magmatic origin of these hornblende-biotite rims, which was largely coeval with the emplacement of the sulfide melt in the magmatic breccias. The formation of the hornblende-biotite rims required the addition of alkalis and water that could not have entirely been sourced from either the sulfide melt or the silicate framework. Through the integration of compositional maps with major and trace element analyses of the main accessory minerals, we propose that the critical components required for the development of the hydrous silicate rims in sulfide-matrix breccias originated from an immiscible Fe-Ti-P melt. Distinct textural and compositional features of apatite, hercynite, ilmenite and magnetite support the presence of small amounts of Fe-Ti-P melt in the sulfide melt. This Fe-Ti-P melt likely formed through melt immiscibility in the early stages of the development of the Voisey’s Bay complex, and was transported in the magma conduits together with the sulfide melt.

The contributions of early potassic and later phyllic alteration stages to Cu endowment of the giant Dexing porphyry Cu–Mo–Au system in South China are determined using changes in the Cu isotope composition of hypogene chalcopyrite from three vein stages. The δ⁶⁵Cu values of chalcopyrite (δ⁶⁵Cu_cpy values) from the potassic (stage 1: -0.05‰ to 0.21‰) to the phyllic alteration stages (stage 2: -0.03‰ to 0.24‰) are relatively invariable, but chalcopyrite in the propylitic alteration stage (stage 3) has notably lower isotopic values (-0.35‰ to 0.02‰). The sharp decrease in δ⁶⁵Cu_cpy values in the latest vein stage is likely a result of precipitation of significant amounts of isotopically heavy chalcopyrite in the phyllic alteration environment. The overall isotopic evolution can be simulated, using a Rayleigh fractionation model, with the majority of Cu having precipitated during the phyllic alteration stage. By comparing our data with published Cu isotope results from other porphyry deposits, we demonstrate that the systematics of δ⁶⁵Cu_cpy values during different hydrothermal alteration stages could convincingly trace the relative timing and mechanism(s) of Cu precipitation in porphyry Cu systems. Spatial mapping of Cu isotopes at Dexing suggest that sharp decreases of δ⁶⁵Cu_cpy values in hypogene zones may be used to delineate the boundary of high-grade ore zones.