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[Display omitted] • Detailed observations reveal three successive generations of sphalerite. • Mineralization is induced by magmatic fluid recharge and mixing of meteoric water. • The GDC deposit belongs to an intermediate-sufidation epithermal mineralization. • Potential of porphyry mineralization is worth expecting in GDC area. The Gongdongchong (GDC) lead and zinc deposit is located in the North Huaiyang (NHY) metallogenic belt, northern part of the Dabie orogen. Its Pb-Zn orebodies are predominately in the breccia pipe hosted by the Early Paleozic Foziling Group. Three stages of mineralization could be divided according to replacement relationships and petrography, and the ore and gangue mineral assemblages at the main base metal stage were recognized as combination of Fe-poor sphalerite + galena + pyrite + chalcopyrite + tetrahedrite with quartz and calcite. Three successive generations of sphalerite were distinguished through detailed petrographic observation on crystal-scale, namely Sp c (core), Sp m (mantle), and Sp r (rim). Fluid inclusion petrography result shows that two-phase liquid-rich fluid inclusions are the dominant type in sphalerite. Microthermometric results show the homogenization temperatures and salinities of Sp c ranged from 233 °C to 268 °C and 6.6 to 10.4 wt% NaCl equiv. While fluid inclusions in the Sp m display homogenization temperatures of 241 °C to 284 °C, with salinities of 8.7 to 11.3 wt% NaCl equiv. This increasing trend may imply a magmatic fluid recharging from core to mantle. However, fluid inclusions in the Sp r have homogenization temperatures of 231–254 °C, with salinities of 6.3–9.1 wt% NaCl equiv. A trend of mixing with meteoric water is manifested by the decrease of temperatures with decreasing salinities from mantle to rim. It suggests the combination of the magmatic fluid recharging and mixing of meteoric water should be the key mechanism responsible for the sphalerite precipitation at the GDC deposit. Meanwhile, the GDC deposit shows a similar range of homogenization temperatures and salinities with typical intermediate-sulfidation epithermal deposits, and these homogenization temperatures also correspond well with the geological thermometer results acquired by trace element concentrations of sphalerite. In addition, the sphalerite geochemical results obtained from trace elements as Mn, Co, In and Ge illustrate that the GDC Pb-Zn deposit shares a good consistence with epithermal Pb-Zn deposit. Based on the evidences presented above, combined with the geological and geochemical features, the GDC deposit can be classified as an intermediate-sulfidation epithermal deposit. Intermediate-sulfidation epithermal deposits usually share spatial and genetic relationships with porphyry deposits. This may provide new implication for the mineral exploration of porphyry deposits at depth in the NHY metallogenic belt. [ABSTRACT FROM AUTHOR]

• LA–ICP–MS analysisof fluid inclusions indicates a common magmatic–hydrothermal fluid source. • Halite bearing fluid inclusions in deep level of quartz veins contain significant amounts of Pb, Zn, and Cu. • Result of fluid inclusion mapping agrees well with the fluid evolution trend obtained through fluid inclusion LA–ICP–MS analysis. The Xianhualing District at Jinzhai in the northern Dabie Orogen, China, is a significant area for Pb–Zn–Cu–Au polymetallic exploration. The main rocks in the area are mica–quartz schist of the Neoproterozoic Foziling Group, and magmatic rocks which are controlled by two sets of faults striking NNE and NW. Recent drilling has revealed that the orebody occurs mainly in mica–quartz schist in the form of breccia and veinlets. Major ore minerals include pyrite, sphalerite, galena, chalcopyrite, magnetite, gold, silver, and silver sulfosalts, with alteration assemblages of predominantly quartz, sericite, calcite, and chlorite. Three types of fluid inclusions occur in quartz–sulfide vein samples collected from eight drill-holes: two-phase liquid-rich inclusions (type I), two-phase vapor-rich inclusions (type Ⅱ), and halite-bearing inclusions (type III). Microthermometric studies of type I and Ⅱ fluid inclusions indicate homogenization temperatures of 161–378 °C and salinities of 0.5–7.8 wt% NaCl equivalent. Fluid inclusion microthermometric data and mineralization and alteration characteristics indicate an intermediate-sulfidation epithermal environment. Current exploration is focused on the location of potential deep porphyry mineralization associated with epithermal mineralization. In this study, 28 drill-core samples from different levels were selected for fluid inclusion microthermometry to elucidate fluid-evolution pathways and hence to determine the likelihood of porphyry bodies. The consistent fluid inclusion petrography, distribution patterns, and fluid-evolution trends indicate that the deeper part of the Dongchong area may have been the regional thermal center of fluid flow. The estimated mineralization depths of type III fluid inclusions are in the range 0.4–1.5 km, indicating a relatively shallow formation. Fluid chemical compositions obtained from single-inclusion laser-ablation–inductively coupled plasma–mass spectrometry (LA–ICP–MS) analyses support the occurrence of a single magmatic–hydrothermal fluid source, which has a degree of mixing with meteoric water and a small amount of basinal brines during the migration path, and the fluid evolution pattern agrees well with the fluid inclusion mapping result. Quartz-vein hosted fluid inclusions contain significant amounts of Pb, Zn, and Cu, indicating good exploration prospects for porphyry Cu mineralization at depth. [ABSTRACT FROM AUTHOR]

[Display omitted] • Two generations of pyrite show distinguished textures and chemical compositions. • These generations likely record an evolution from non-immiscibility to immiscibility. • The key factor for the Au precipitation is fluid immiscibility in the second stage. • The immiscibility is responsible for the unusual decoupling of Au and As in pyrite. Pyrite, as one of the most important Au carriers, can well document ore-forming processes. In this study, we select the Hekou gold deposit (HKGD), a newly discovered deposit in the North China Craton (NCC), to rebuild its ore-forming process and gold precipitation mechanism with pyrite. The gold-bearing pyrite was used to perform a combined micro-textural petrography, elemental and S isotope analyses. The micro-textural petrography reveals two distinguished generations of pyrite, including coarse-grained euhedral Py1 and fine-grained xenomorphic Py2. The fine-grained xenomorphic Py2 likely results from a fast nuclear rate responding to the rapid thermochemical changes of hydrothermal fluid. Trace elements of pyrite constrained by LA-ICP-MS reveal that the concentrations of metals such as Au, Ag, Cu, and Pb dramatically increase from Py1 to Py2, suggesting that the fluid evolved to oversaturation. The concentrations of As notably decrease from 284.35 to 23.27 ppm from Py1 to Py2, supporting that As escape from the ore solutions. Moreover, the in situ S isotopes by LA-MC-ICP-MS reveal a minor δ34S fractionation between Py1 (6.29±0.22‰, 2SD) and Py2 (5.95±0.22‰, 2SD), which also agree with the isotopic behavior of H 2 S escape. All of them, together with fluid inclusion observation, we explain that the two-stage pyrite formation in the HKGD records a hydrothermal system evolution from non-immiscibility (Py1) to immiscibility (Py2). Fluid immiscibility likely effectively facilitated the Au precipitation in the HKGD, via significantly destabilizing the Au-HS complex in fluid and incorporating Au into pyrite. Meanwhile, it also led to an unusual decoupling of Au and As in pyrite. This study highlights that the pyrite texture and chemistry can be excellent tools to reveal trace hydrothermal system evolution and gold precipitation mechanism. [ABSTRACT FROM AUTHOR]

[Display omitted] • The hydrothermal process is divided into four stages from early to late, and two stages of Sn mineralization are identified. • Fluid mixing may be the predominant mechanism for the minor Sn mineralization occurred in stage II. • Fluid cooling may be the predominant mechanism for the abundant cassiterite precipitation in stage III. • The ore-forming fluid mainly derived from highly evolved granitic magma, and the genesis of cassiterite is consistent with typical skarn-type Sn deposits. The Xianghualing Sn-polymetallic deposit is a large skarn-type Sn deposit located in the Nanling polymetallic metallogenic belt, South China. The ore bodies are controlled by NE-trending faults and mainly hosted in the contact of Middle Devonian carbonate rock and granite. The Xianghualing deposit is divided into four mineralization stages, and two stages of Sn mineralization are identified. The mineralization stages from early to late include stage I (prograde stage), stage II (retrograde stage), stage III (cassiterite-magnetite-arsenopyrite-topaz-quartz stage), stage IV (sphalerite-galena-pyrite-chalcopyrite-quartz-calcite stage). Stage II is the initial stage of Sn mineralization where only minor cassiterite precipitates, and stage III is the main Sn mineralization stage where abundant cassiterite precipitates. On this basis, fluid inclusion microthermometry and Raman spectroscopy analyses were carried out for ore and/or gangue minerals at different stages. In addition, trace element composition analysis was also conducted on cassiterite. These data can contribute to reveal the fluid properties, evolution and formation mechanism of Xianghualing deposit. Three types of fluid inclusions were identified in different mineralization stages, including halite-bearing multi-phase inclusions (Type B), liquid-rich two-phase inclusions (Type L) and vapor-rich two-phase inclusions (Type V). Garnet (stage I) contains Type B inclusions and Type V inclusions, with homogenization temperatures and salinities of 511–549 °C, 37.6–48.9 wt% NaCl equiv. and 551–559 °C, 4.0–5.1 wt% NaCl equiv., respectively. Topaz (stage II) contains Type L inclusions with homogenization temperatures of 408–445 °C and salinities of 9.5–12.4 wt% NaCl equiv. Cassiterite (stage III) contains Type L inclusions with homogenization temperatures of 368–417 °C and salinities of 8.7–11.5 wt% NaCl equiv. Quartz (stage IV) contains Type L inclusions with homogenization temperatures of 162–227 °C and salinities of 2.6–5.0 wt% NaCl equiv. The temperature and salinity of the fluid from stage I to stage II decreased significantly, recording intense meteoric water mixing. The temperature of the fluid decreased from stage II to stage III, while the salinity changed little, indicating that, except for minor meteoric water mixing, cooling of fluid is predominant. The temperature and salinity of the fluid from stage III to stage IV continued to decrease, recording the further mixing of meteoric water. From stage II to stage III, the evolution temperature of the fluid is basically consistent with the temperature indicated by trace elements (Nb, Ta, Ti) of cassiterite in the two stages. Fluid mixing may be the predominant mechanism for the minor Sn mineralization occurred in stage II. Fluid cooling may be the predominant mechanism for the abundant cassiterite precipitation in stage III, which is accompanied by redox reactions of Sn (II)-Cl complexes with As (III) and/or CO 2 as potential oxidants, and acid neutralization of carbonate rocks. Combined with the cassiterite composition, it is indicated that the ore forming fluid of the Xianghualing deposit mainly derived from the highly evolved granitic magma in the region, and the genesis of cassiterite is consistent with that of typical skarn-type Sn deposits. [ABSTRACT FROM AUTHOR]