Whether giant porphyry ore deposits are the products of single, short-lived magmatic-hydrothermal events or multiple events over a prolonged interval is a topic of considerable debate. Previous studies, however, have all been devoted to porphyry Cu and Cu-Mo deposits. In this paper, we report high-precision isotope dilution-negative-thermal ionization mass spectrometric (ID-N-TIMS) molybdenite Re-Os ages for the newly discovered, world-class Chalukou porphyry Mo deposit (reserves of 2.46 Mt @ 0.087 wt % Mo) in NE China. Samples were selected based on a careful evaluation of the relative timing of the different vein types (i.e., A, B, and D veins), thereby ensuring that the suite of samples analyzed could be used to reliably determine the age and duration of mineralization. The molybdenite Re-Os geochronology reveals that hydrothermal activity at Chalukou involved two magmatic-hydrothermal events spanning an interval of 6.92 ± 0.16 m.y. The first event (153.96 ± 0.08/0.63/0.79 Ma, molybdenite ID-N-TIMS Re-Os age) was associated with the emplacement of a granite porphyry dated at 152.1 ± 2.2 Ma (zircon laser ablation-inductively coupled plasma-microscopic [LA-ICP-MS] U-Pb ages), and led to only minor Mo mineralization, accounting for <10% of the overall Mo budget. The bulk of the Mo (>90%) was deposited in less than 650 kyr, between 147.67 ± 0.10/0.60/0.76 and 147.04 ± 0.12/0.72/0.86 Ma (molybdenite ID-N-TIMS Re-Os ages), coincident with the emplacement of a fine-grained porphyry at 148.1 ± 2.6 Ma (zircon LA-ICP-MS U-Pb ages). The high-precision Re-Os age determinations presented here show, contrary to the finding of a number of studies of porphyry Cu and Cu-Mo systems, that the giant Chalukou porphyry Mo deposit primarily formed in a single, short-lived (<650 kyr) hydrothermal event, suggesting that this may also have been the case for other giant porphyry Mo deposits.

Cinnabar (α-HgS) is the most common sulfide of mercury while metacinnabar (β-HgS), a high-temperature homogeneous polymorph of the mercury sulfide, is relatively rare, and the α phase of cinnabar transforms to the β phase at 344 °C. Meanwhile, there is a complete isomorphic series between HgS and HgSe, and the occurrence of Se-bearing metacinnabar is of great significance for the exploration of selenium resources. We studied through microscopic observation, electron-probe microanalysis, X-ray diffraction and field emission scanning electronic microscopy (FESEM) the Se-bearing metacinnabar of the Wanshan mercury ore field of southeastern Yangtze Block. These analyses, combined with physicochemical phase diagrams, constrained the textural and chemical evolution during the formation process of Se-bearing metacinnabar. Se-bearing metacinnabar was found in altered carbonatite, intergrown with cinnabar, sphalerite, pyrite, realgar and quartz. The Se-bearing metacinnabar contains 77.66–84.01 wt.% Hg, 0.18–1.17 wt.% Zn with extensive isomorphic substitution of Se and S (2.79–14.77 wt.% Se, 6.15–11.82 wt.% S). The presence of impurity elements (e.g., Zn and Se) is considered to be the key factor in expanding the stable range of Se-bearing metacinnabar. The cinnabar generated by the transformation of Se-bearing metacinnabar is characterized by inclusions of Hg-bearing sphalerite and pores, which indicate that this process was carried out through a coupled dissolution–reprecipitation (CDR) reaction. The formation temperature of Se-bearing metacinnabar is higher than that of cinnabar, and according to the phase relations between sulfides and selenides, we propose that logfS2(g) of ore-forming fluids is constrained within −15.663 to −13.141, and logfSe2 < logfS2–3.994 (150 °C).

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Porphyry type Mo deposits have supplied most of the Mo to the world. However, the source of the Mo and the controls on its enrichment in such deposits is still a matter of great debate. In this study, we present in situ trace element and isotopic data for a giant porphyry Mo deposit (the Chalukou Mo deposit in NE China) and use these data to address these issues. Three primary paragenetic stages of mineralization were recognized at Chalukou: (I) K-feldspar + quartz + minor pyrite (Py-I) + minor molybdenite (Mol-I); (II) quartz + sericite + molybdenite (Mol-II) + pyrite (Py-II); (III) quartz + chlorite + epidote + fluorite + pyrite (Py-III) + galena + sphalerite + minor chalcopyrite. The bulk of the molybdenite was deposited in Stage II. In situ S isotope analyses of the sulfide ores show that the δ 34 S values vary from -5.2 to +7.8‰ (mean = +2.9‰), and correspond to δ 34 S H2S values from -2.4 to +3.3‰ (mean = +1.1‰). These values are consistent with a magmatic source for the sulfur. In situ Pb isotope compositions of the sulfide ores are almost identical to those of the local Mesozoic granites and other magmatic-hydrothermal ore deposits in this region, suggesting a close genetic association between the Mo mineralization and felsic magmatism.Pyrite from the three stages of mineralization differs significantly in its trace element composition. The first generation, Py-I, has a high Cu content (8.7 ± 49.6 ppm; where the first value is the median and the second is the standard deviation) and Mo content (6.9 ± 3.8 ppm). Pyrite-II has the lowest Cu concentration (1.3 ± 2.1 ppm) and a relatively high Mo concentration (5 ± 128 ppm), and Py-III has a high Cu This is the peer-reviewed, final accepted version for American Mineralogist, published by the Mineralogical Society of America.The published version is subject to change. Cite as Authors (Year) Title. American Mineralogist, in press.

The Beiya gold deposit (323t of gold @ 2.47 g/t) is located in the centre of the Jinshajiang‐Ailaoshan potassium alkaline porphyry Cu‐Au metallogenic belt in SW China, which is the largest skarn gold deposit in China. As the dominant ore mineral at Beiya, magnetite has been selected as a petrogenetic indicator to understand the ore‐forming process. In this study, magnetites have been divided into the euhedral–subhedral (ME), anhedral (MA), lamellar (ML), and replaced (MR) types based on their textures, which have been further determined by in situ laser ablation inductively coupled plasma mass spectrometry analyses. In detail, plots in discriminant diagrams constrain the Beiya magnetite a hydrothermal origin. Trace elements in magnetite vary with respect to different textures. Titanium concentrations are similar in all magnetite types, suggesting that all magnetites were precipitated in a relatively narrow temperature range. The decreasing V content combined with haematite after magnetite (martitization) suggests that the oxygen fugacity increased from ME and MA and then decreased to ML and MR. All magnetite types show similar content variations and similar (Mg + Mn)/Al ratios, indicating a decreasing degree of fluid–rock interactions. The rim–core texture indicates that the MR type magnetite has experienced the dissolution–reprecipitation process. Mushketovite marks the later ore‐forming environment and the iron‐rich hydrothermal fluids transformed from high temperature and oxidized to low temperature and reduced features. Magnetite textures, combined with its trace element variations, could be used as a potential tool for inferring the ore‐forming fluid evolution.