Diversity of Pyrite-Hosted Solid Inclusions and their Metallogenic Implications—A Case Study from the Myszków Mo–Cu–W Porphyry Deposit (the Kraków–Lubliniec Fault Zone, Poland)

Pyrite from the central part of the Myszków porphyry deposit in Poland was investigated using a combination of reflected and transmitted polarizing microscopy, back-scattered imaging with energy-dispersive X-ray spectroscopy, and Raman micro-spectroscopy. Five generations of pyrite (I–V) found in hydrothermal veins were distinguished, differing in morphology, microtexture, and the types and amounts of solid inclusions. In general, pyrite hosts a diversity of mineral inclusions, including both gangue and ore phases, i.e., chlorite, quartz, monazite, cerianite-(Ce), xenotime, K-feldspars, albite, sericite, barite, magnetite, chalcopyrite, galena, sphalerite, bastnaesite (Ce), bismuthinite, native silver, cassiterite, rutile, anatase, and aikinite-group species. The presence of inclusions is good evidence of various stages of the evolution of the hydrothermal lode system ranging from high- to low-temperature conditions. During the formation of stockworks, some fluctuations in the physicochemical conditions of mineralizing fluids were indicated by the occurrence of cassiterite formed from acidic, reducing solutions, and hematite hosted in xenotime or REE phases found in pyrite, which signal more oxidizing conditions. Periodically, some episodes of boiling in the hydrothermal, porphyry-related system were recorded. They were mainly evidenced by the presence of (1) lattice-bladed calcite found in the close vicinity of pyrite II, (2) irregular grain edges of pyrite I, (3) clustered micropores in pyrite I, and (4) the variety of mineral inclusions hosted in I and II generations of pyrite.

The Metallogeny of the Tieling Cu-Mo Porphyry Deposit in Eastern Tianshan, NW China: New Insights from Zircon U-Pb, Fluid Inclusion, and H-O-S Stable Isotope Analyses

The eastern Tianshan metallogenic belt is an important molybdenum resource base in Xinjiang and is characterized by large-scale porphyry Mo deposits formed during the Triassic. The Tieling Cu-Mo porphyry deposit, which is situated in the western part of the eastern Tianshan metallogenic belt, was recently recognized as being related to Carboniferous granite porphyry. Three stages of hydrothermal mineralization were identified, including quartz+K-feldspar+pyrite±molybdenite±magnetite (stage I), quartz+molybdenite+pyrite+chalcopyrite (stage II), and quartz+pyrite±molybdenite±epidote (stage III). Fluid inclusion petrography and microthermometry analyses indicate the presence of gas-liquid inclusions with a H2O-NaCl composition. The ore-forming fluids have a characteristic temperature ranging from 157 to 262°C under stage II and 135 to 173°C under stage III, which correspond to salinities of 7.2-17.2 wt% NaCl equiv. and 5.9 to 9.6 wt% NaCl equiv., respectively. The hydrogen and oxygen isotope data indicate that the ore-forming fluids of the Tieling deposit were originally derived from magmatic hydrothermal fluids and then mixed with meteoric water. The sulfur isotope compositions indicate that the ore-forming materials were mainly derived from the Late Carboniferous felsic magma. Furthermore, zircon U-Pb analysis of ore-bearing granite porphyry yields a concordant age of 298.4 ± 0.7 Ma , indicating that the Tieling Cu-Mo deposit formed during the Late Carboniferous and differed from that processed under pre-Early Carboniferous and Triassic mineralization in the eastern Tianshan metallogenic belt. These results also indicate that the Tieling porphyry deposit was formed in the transition condition between subduction-related accretion and postcollisional orogeny, and it should be given more attention in prospect evaluations.

Zircon Petrochronology of the Kişladaǧ Porphyry Au Deposit (Turkey)

Porphyry deposits typically occur in subduction-related arcs but have more recently also been described in postsubduction, collisional to extensional back-arc settings. These different tectonic environments not only might imply different genetic processes but also seem to result in different metal endowments (e.g., Au rich versus Cu rich). It is therefore relevant, also for exploration purposes, to understand the magmatic processes involved in porphyry formation in these different tectonic environments. This study focuses on the Kişladaǧ porphyry Au (17.4 Moz) deposit in western Anatolia, which is centered on a series of porphyritic monzonite stocks of high-K calc-alkaline to shoshonitic affinity and formed in a continental rifting environment. With 17.4 Moz of Au, Kişladaǧ is of global metallogenic importance and hence a good example for studying the genetic processes associated with porphyry deposits in extensional back-arc settings. We herein combine a comprehensive set of new zircon textural observations, in situ zircon trace element and Hf isotope data, and previously published zircon geochronology to study the magmatic processes associated with porphyry deposit formation at Kişladaǧ. We show that mafic rejuvenation of a slowly crystallizing (between ~15.8 and 14.9 Ma) magma reservoir below Kişladaǧ immediately preceded porphyry deposit formation. Zircon trace elements and geochronology suggest a longer and deeper evolution for the early fertile magmas compared to the later infertile magmas. Magma evolution at Kişladaǧ was accompanied by crustal wall-rock assimilation. Whole-rock Nd and Sr radiogenic isotopes show that increasing asthenosphere-derived melt input under accelerated regional extension caused a loss in fertility of the system over time.

Integration of Dual Border Effects in Resource Estimation: A Cokriging Practice on a Copper Porphyry Deposit

Hierarchical or cascade resource estimation is a very common practice when building a geological block model in metalliferous deposits. One option for this is to model the geological domains by indicator kriging and then to estimate (by kriging) the grade of interest within the built geodomains. There are three problems regarding this. The first is that sometimes the molded geological domains are spotty and fragmented and, thus, far from the geological interpretation. The second is that the resulting estimated grades highly suffer from a smoothing effect. The third is related to the border effect of the continuous variable across the boundary of geological domains. The latter means that the final block model of the grade shows a very abrupt transition when crossing the border of two adjacent geological domains. This characteristic of the border effect may not be always true, and it is plausible that some of the variables show smooth or soft boundaries. The case is even more complicated when there is a mixture of hard and soft boundaries. A solution is provided in this paper to employ a cokriging paradigm for jointly modeling grade and geological domains. The results of modeling the copper in an Iranian copper porphyry deposit through the proposed approach illustrates that the method is not only capable of handling the mixture of hard and soft boundaries, but it also produces models that are less influenced by the smoothing effect. These results are compared to an independent kriging, where each variable is modeled separately, irrespective of the influence of geological domains.

Arsenical native copper from Au-Cu porphyry Ak-Sug deposit, Eastern Tyva

The geology of the Ak-Sug Au-Cu-porphyry deposit in the eastern Tyva is considered. The distribution of native copper in ores of the deposits was studied. It has been established that the native copper is of both hypogene and supergene origin. The hypogene native copper is characterized by an elevated arsenic content (up to 4.4 %) and occurs in association with copper arsenides, native silver, zircon, brannerite, xenotime-(Y), florensite-(Ce), chalcocite, and berzelianite. Hypogene native copper is confined to ore schistosity zones .

Assessing physical and mechanical properties of enclosing rock in the course of Malmyzhskoe gold-copper-porphyry deposit development

Introduction. This work presents the results of complex technological and mineralogical studies. It has been discovered that some natural rocks are characterized by physical and mechanical properties variability 58 "Izvestiya vysshikh uchebnykh zavedenii. Gornyi zhurnal". No. 3. 2021 ISSN 0536-1028 even within a local area. It must be taken into account when assessing enclosing rocks utilization options. The results of Malmyzhskoye rock physical and mechanical properties study at the stage of geological exploration are considered. Research aim is to carry out integrated technological and mineralogical research and laboratory tests on rock physical and mechanical properties to assess the feasibility of using hard enclosing rock for construction. Research methodology. The geological and structural features of the field were established by comparative analysis of geological sections and maps, structural documentation of the core. In laboratory conditions, the physical and mechanical properties of the host rocks that make up the gold-copper-porphyry deposit were established. Results. After studying the mineral (chemical) composition and physical and mechanical properties of rocks, it was possible to obtain the dependence of the strength index on the structure, as well as on the content of dark-colored minerals and plagioclases. At the same time, there are no significant correlations between strength and density within the same rock type. Conclusions. The analysis shows that rocks with the same mineral composition and equal values of the true density, but with different texture and structure, show differences in strength properties. Keywords: Malmyzhskoe deposit; breakability; physical and mechanical properties; rocks; petrographic analysis; density; strength.

Isotopic spatial-temporal evolution of magmatic rocks in the Gangdese belt: Implications for the origin of Miocene post-collisional giant porphyry deposits in southern Tibet

Crustal growth is commonly associated with porphyry deposit formation whether in continental arcs or collisional orogens. The Miocene high-K calc-alkaline granitoids in the Gangdese belt in southern Tibet, associated with porphyry copper deposits, are derived from the juvenile lower crust with input from lithospheric mantle trachytic magmas, and are characterized by adakitic affinity with high-Sr/Y and La/Yb ratios as well as high Mg# and more evolved isotopic ratios. Researchers have argued, lower crust with metal fertilization was mainly formed by previous subduction-related modification. The issue is that the arc is composed of three stages of magmatism including Jurassic, Cretaceous, and Paleocene−Eocene, with peaks of activity at 200 Ma, 90 Ma, and ca. 50 Ma, respectively. All three stages of arc growth are essentially similar in terms of their whole-rock geochemistry and Sr-Nd-Hf isotopic compositions, making it difficult to distinguish Miocene magma sources. This study is based on ∼430 bulk-rock Sr-Nd isotope data and ∼270 zircon Lu-Hf isotope data and >800 whole-rock geochemistry analyses in a 900-km-long section of the Gangdese belt. We found large scale variations along the length of the arc where the Nd-Hf isotopic ratios of the Jurassic, Cretaceous, and Paleocene−Eocene arc rocks change differently from east to west. A significant feature is that the spatial distribution of Nd-Hf isotopic values of the Paleocene−Eocene arc magmas and the Miocene granitoids, including metallogenic ones, are “bell-shaped” from east to west, with a peak of εNd(t) and εHf(t) at ∼91°E. In contrast, the Jurassic and Cretaceous arc magmas have different isotopic distribution patterns as a function of longitude. The isotopic spatial similarity of the Paleocene−Eocene and Miocene suites suggests that the lower crust source of the metallogenic Miocene magmas is composed dominantly of the Paleocene−Eocene arc rocks. This is further supported by abundant inherited zircons dominated by Paleocene−Eocene ages in the Miocene rocks. Another important discovery from the large data set is that the Miocene magmatic rocks have higher Mg# and more evolved Sr-Nd-Hf isotopic compositions than all preceding magmatic arcs. These characteristics indicate that the involvement of another different source was required to form the Miocene magmatic rocks. Hybridization of the isotopically unevolved primary magmas with isotopically evolved, lithospheric mantle-derived trachytic magmas is consistent with the geochemical, xenolith, and seismic evidence and is essential for the Miocene crustal growth and porphyry deposit formation. We recognize that the crustal growth in the collisional orogen is a two-step process, the first is the subduction stage dominated by typical magmatic arc processes leading to lower crust fertilization, the second is the collisional stage dominated by partial melting of a subduction-modified lower crust and mixing with a lithospheric mantle-derived melt at the source depth.