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• The first in-situ LA–ICP–MS dating of titanite in the A vein of porphyry deposits has been analyzed in polished thin section. • The titanite dating data (44.4 ± 1.5 Ma) in the A1 vein of the Lancang Laochang polymetallic deposit further delineates the evolutionary timeline from magma to ore-forming fluid in 45–43 Ma. • From magma to the initial ore-forming fluid in the Laochang deposit, a slightly pressure increase (from 93 MPa to 98 MPa) and a minor decrease of temperature (from 697 °C to 680 °C) and log f O 2 (from −16.78 to −17.29) have been revealed. The Laochang polymetallic deposit is the only large deposit in the Changning–Menglian Junction Zone. The deposit features by deep porphyry-skarn Mo–(Cu) and shallow vein Pb–Zn–(Ag) mineralization. Researches on the deposit have yielded extensive data, however, details about the initial evolution from magma to ore-forming fluid remain unclear. This study centers on the in-situ analysis of biotite from the porphyry, as well as phlogopite and titanite from the A vein, leading to the following insights: (1) The biotite geothermobarometer suggests the porphyry intruded in a moderate depth (2.57–4.27 km), with average parameters as P = 93 MPa, T = 697 °C, and log f O 2 = -16.78. (2) The A vein in the deposit can be further subdivided into A1 K-feldspar vein and A2 quartz vein. The phlogopite in the A1 vein formed at P = 98 MPa, T = 681 °C, and log f O 2 = -17.29. The pressure of the A1 vein is slightly higher than the static pressure of wall rock, attributed to pressure increment from the initial exsolved fluid. Conversely, the temperature and oxygen fugacity experience a slight decrease, due to buffering of the adjacent tuff. (3) The in-situ LA–ICP–MS U–Pb dating of the titanite in the A1 vein yields 44.4 ± 1.5 Ma (MSWD = 1.8, n = 48), comparable to the emplacement age of the porphyry (44.6–44.4 Ma). It is slightly older than the main mineralization age (43.78 Ma), further delineated the initial evolution sequence from magma to ore-forming fluid. Our research suggests that the in-situ analysis of titanite is crucial for preciously tracking the magma–fluid system, as titanite records both time and temperature information. [ABSTRACT FROM AUTHOR]

• Eocene-Oligocene (36–33 Ma) potassic felsic rocks occur in the Sanjiang Region. • Eocene potassic felsic rocks produced by partial melting of mafic rocks in a thickened lower crust. • Eocene magmatic activities caused by post-orogenic delamination of lithospheric mantle and asthenosphere upwelling in the Eocene. This study presents zircon U-Pb dating and Hf isotope, whole-rock geochemistry and Sr-Nd isotopes of the potassic felsic porphyries from western Yunnan in the Sanjiang Region. Zircon U-Pb dating reveals that quartz-monzonite porphyry, granite porphyry, and adakitic granite porphyry were emplaced during 36–33 Ma. Geochemical data show that quartz-monzonite and granite porphyries have enriched LREE ((La/Yb) N = 39–67)and depleted HFSEs (e.g. Nb, Ta, P and Ti), with weak Eu anomalies. Moreover, they display similar 87Sr/86Sr ratios of 0.7068–0.7070 and negative εNd(t) values of −6.7 to −5.4, with zircon εHf(t) values of −5.65 to 3.06. The adakitic granite porphyries have high Sr (1273–1377 ppm), low Y (9.2–10.7 ppm), and low Yb (0.9–1.0 ppm) contents and high Sr/Y (128–138) and (La/Yb) N (17.7–19.8) values, typical of adakite rocks. In addition, these adakitic granite porphyries possess negative whole-rock εNd(t) values −0.2 to −0.3 and positive zircon εHf(t) values 2.7–6.0, associated with low Mg#, MgO, Ni and Cr contents. These geochemical features suggest that three kinds of potassic felsic porphyries could be produced by partial melting of mafic rocks (e.g., amphibolite) in a thickened lower crust. Our data, combined with previous studies and regional geology, suggest that delamination of lithospheric mantle and asthenosphere upwelling beneath the Sanjiang Region, both contributed to Cenozoic magmatic activities. [ABSTRACT FROM AUTHOR]

The Late Cretaceous Hongniu–Hongshan porphyry–skarn copper deposit is located in the Zhongdian area of northwestern Yunnan Province, China. Garnets from the deposit have compositions that range from Adr 14 Grs 86 to almost pure andradite (Adr 98 Grs 2 ) and display two different styles of zoning. The garnets are predominantly of magmatic-hydrothermal origin, as is evidenced by their 18 O fluid (5.4–6.9‰) and low D fluid (−142‰ to −100‰) values, both of which likely result from late-stage magmatic open-system degassing. Three generations of garnet have been identified in this deposit: (1) Al-rich garnets (Grt I; Adr 22–57 Grs 78–43 ) are anisotropic, have sector dodecahedral twinning, are slightly enriched in light rare earth elements (LREEs) compared with the heavy rare earth elements (HREEs), have negative or negligible Eu anomalies, and contain high concentrations of F. Fluid inclusions within these Al-rich garnets generally have salinities of 12–39 wt.% NaCl eq. and have liquid–vapor homogenization temperatures (Th) of 272–331 °C. The Grt I are most likely associated with low- to medium-salinity fluids that were generated by the contraction of an ascending vapor phase and that formed during diffusive metasomatism caused by pore fluids equilibrating with the host rocks at low W/R (water/rock) ratios. These garnets formed as a result of the high F activity of the system, which increased the solubility of Al within the magmato-hydrothermal fluids in the system. (2) Fe-rich garnets (Adr 75–98 Grs 25–2 ) have trapezohedral faces, and are both anisotropic with oscillatory zoning and isotropic. These second-generation Fe-rich garnets (Grt II) have high ΣREE concentrations, are LREE-enriched and HREE-depleted, and generally have positive but variable Eu anomalies. All of the Fe-rich garnets contain high-salinity fluid inclusions with multiple daughter minerals with salinities of 33–80 wt.% NaCl eq. Some of them show higher temperatures of halite dissolution (465–591 °C) than liquid–vapor homogenization temperatures (319–473 °C), and several Fe-rich garnets contain inclusion groups indicative of boiling. The Grt II are associated with high-temperature, hypersaline fluids that were segregated from magma at a depth of at least 5.6 km and reacted with carbonates at depths shallower than 2.0 km. (3) Al-rich garnet veins (Adr 14–60 Grs 86–40 ) contain allotriomorphic crystals, have lower HFSE (high field strength element) and REE concentrations than the other garnets, and have HREE-enriched and LREE-depleted patterns with small Eu anomalies that are typical of the majority of garnets. The Grt III most likely formed from residual metasomatic fluids. [ABSTRACT FROM AUTHOR]

Abstract: Although most porphyry-type deposits are associated with subduction-related magmas within magmatic arc settings, recent research has identified a number of porphyry-type deposits that formed in post-subduction tectonic settings. The newly discovered Habo porphyry Cu–(Mo–Au) deposit in Yunnan, China, formed in a post-subduction tectonic setting and is located in the southwest of the Cenozoic Ailao Shan–Red River continental collision zone. The deposit is associated with the Habo South granite pluton, which consists of three mineralization-related quartz monzonite porphyries and a post-mineralization diorite porphyry. Zircons from the Habo South granite and quartz monzonite porphyries were analyzed by in situ U–Pb LA-ICP-MS, yielding a similiar age of 36Ma, with molybdenite Re–Os isotope dating indicating that the Habo porphyry deposit formed at 35.5Ma. Both magmatism and the associated mineralization at Habo are coeval with porphyry copper deposits in the Yulong metallogenic belt of Eastern Tibet. The Habo South granite and porphyries have SiO2 concentrations of 67.28–73.44wt.%, MgO concentrations of <1.5wt.%, Al2O3 concentrations around 15wt.%, Al2O3/(CaO+Na2O+K2O) (A/CNK) ratios of >1.1, K2O+Na2O concentrations generally between 7 and 9wt.%, and K2O/Na2O ratios of >1.4, showing indicative of high-K magmas. The Habo South granite and quartz monzonite porphyries are enriched in light rare earth elements (LREE) and large ion lithophile elements (LILE), and depleted in heavy rare earth elements (HREE) and high field strength elements (HFSE), with high Sr and low Y concentrations. They have initial 87Sr/86Sr values of 0.7071–0.7083, with ε Nd(t) values from −5.3 to −3.7. These features are indicative of lower-crust derived adakitic magmas, and are similar to those of mineralized porphyries in the Yulong copper belt in Eastern Tibet. This mineralogical, geochemical, and isotope evidence strongly suggests that the magmas that formed both porphyries and the Habo South granite were derived by partial melting of a region of thickened lower crust, with assimilation of components generated from a region of phlogopite-bearing lithospheric mantle involved during intrusion. The Habo porphyry deposit represents an extension of the Yulong metallogenic belt and formed in response to regional tectonic activity in Eastern Tibet. [Copyright &y& Elsevier]

Highlights: [•] The diorite porphyry in the Hongniu-Hongshan Cu deposit formed at 200Ma. [•] The quartz monzonite porphyry in the Hongniu-Hongshan Cu deposit formed at 77Ma. [•] The molybdenite Re–Os isotopic date of the ore is 78.9Ma. [•] The quartz monzonite porphyry formed by the remelting of the residual oceanic slab. [ABSTRACT FROM AUTHOR]

Abstract: The origin of zonal mineralization in porphyry copper deposit is important for understanding the mineralization processes. We propose a new, modified “orthomagmatic” genetic model for mineralization zoning in hypogene porphyry copper deposits. This new model is based on the features and formation mechanism of comb microfractures in quartz–chalcopyrite veins within pyrite vein from the Hongshan porphyry copper deposit in Zhongdian County, western Yunnan Province, SW-China. The main evidence for this model is volume expansion related to crystallization of chalcopyrite, magnetite and K-metasomatism in the deposit. Comb microfractures are well developed in quartz–chalcopyrite veins and are present as comb-quartz veinlets consisting of a zone of central longitudinal quartz overprinted by laterally grown quartz combs. Chalcopyrite fragments lie perpendicular to the central quartz veinlet and were dismembered by the quartz combs. The combed microfractures are typical tensional hydrofractures. The formation of the comb microfractures is related to volume expansion that was induced by crystallization of chalcopyrite from a chalcopyrite melt that resulted in the subsequent increase of volumetric pressure in the confined residual silica melt. The formation mechanism of the comb microfractures, including volume expansion induced by crystallization, increases volumetric pressure, hydrofracturing and fluid expulsion, and was the most likely process for zoning of minerals in hypogene porphyry copper deposits. Fabrics in the veins and veinlets are consistent with overpressuring and injection and are common structures that are directly related to volumetric pressure and crystallization of chalcopyrite and magnetite and K-metasomatism in hypogene porphyry copper deposits. The volume expansion ratio of chalcopyrite mineral to melt and that of magnetite mineral to melt are approximately 19vol.% and 20vol.%, respectively. The volume expansion rate of a monomolecular lattice is ⩾8vol.% for orthoclase replacing plagioclase. We suggest that zoning of mineralization in hypogene porphyry copper deposits is mainly related to hydrofracturing, migration and distribution of ore-forming fluids, including (1) the enclosure and formation of a mush core, (2) concentration of ore-forming fluids in the orthoclase shell, (3) K-metasomatism and pressure building, (4) hydrofracturing and migration of ore-forming fluids, and (5) prior crystallization of magnetite and chalcopyrite that will expel residual fluids upwards and outwards due to the change in volumetric pressure. [Copyright &y& Elsevier]