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Understanding the magmatic-hydrothermal cooling and exhumation history is fundamental for investigating porphyry deposit formation and preservation. In the Zhunuo porphyry copper deposit of southern Tibet, hydrothermal biotite related to early potassic alteration likely formed from 14.7 ± 0.3 Ma (zircon U-Pb age) to 14.23 ± 0.13 Ma (molybdenite Re-Os age) and cooled below the closure temperature for 40Ar/39Ar system at 13.91 ± 0.05 Ma (hydrothermal biotite 40Ar/39Ar plateau age). The 40Ar/39Ar spectra of another hydrothermal biotite sample that was selectively replaced by chlorite record the timing of late phyllic alteration at 13.53 ± 0.08 Ma. Zhunuo hydrothermal alteration and mineralization likely ceased at 13.09 ± 0.07 Ma based on the 40Ar/39Ar plateau age of the fresh magmatic biotite crystals. The biotite 40Ar/39Ar systematics have not been reset by ~ 12.0 Ma post-mineralization granite porphyry within ore district, which is likely due to rapid cooling and/or absence of fluid exsolution for the granite porphyry. In combination with previous zircon U-Pb and molybdenite Re-Os data, two-pulses of magmatic-hydrothermal activity from 14.78 ± 0.11 to 14.44 ± 0.05 Ma and from 14.23 ± 0.13 to 13.53 ± 0.08 Ma can be recognized at Zhunuo. (U-Th)/He thermochronological data on zircon and apatite from the inter-mineralization monzogranite porphyry suggest three cooling events characterized by first-stage magmatic cooling at a rate of ~ 1850 °C/m.y., and two later phases of uplift and exhumation at ~ 70 °C/m.y. and ~ 10 °C/m.y. Approximately 1.4-km thickness of materials have been removed from the Zhunuo Miocene monzogranite porphyry during uplift and erosion, including a large volume of ore. [ABSTRACT FROM AUTHOR]

Diabases from the Zhaxikang Sb–Pb–Zn–Ag deposit in southeastern Tibet provide an opportunity to reveal the tempo‐spatial distribution of the recently identified Comei large igneous province and understand the association with Zhaxikang mineralization. Here we present whole‐rock geochemical and Sr–Nd–Re–Os isotopic data on the Zhaxikang diabases. The Zhaxikang diabases have a Re–Os isochron age of 136.1 ± 3.1 Ma. These rocks are characterized by high TiO2 content (3.0–4.2 wt%) and have alkaline ocean island basalt‐like trace element patterns with initial 87Sr/86Sr ratios of 0.7060–0.7069, εNd(t) values of 1.3–3.3, and 187Os/188Os(t) ratios of 0.12–0.13. The Zhaxikang diabases are part of the Comei large igneous province and were derived from partial melting of enriched garnet‐bearing mantle source and related to interaction of plume melts with subcontinental lithospheric mantle. Our new data provided additional evidence that Zhaxikang Pb–Zn(Ag)‐bearing Mn–Fe carbonate veins were not produced by a sedimentary exhalative event in Triassic–Jurassic rift environment. [ABSTRACT FROM AUTHOR]

Several Au, Sb, Sb–Au, Pb–Zn, and Sb–Pb–Zn–Ag deposits are present throughout the North Himalaya in southern Tibet, China. The largest Sb–Pb–Zn–Ag deposit is Zhaxikang (18 Mt at 0.6 wt% Sb, 2.0 wt% Pb, 3.5 wt% Zn, and 78 g/t Ag). Zhaxikang veins are hosted within N–S trending faults, which crosscut the Early–Middle Jurassic Ridang Formation consisting of shale interbedded with sandstone and limestone deposited on a passive continental margin. Ore paragenesis indicates that Zhaxikang mineralization occurred in two main phases composed of six total stages. The initial phase was characterized by assemblages of fine-grained Mn–Fe carbonate + arsenopyrite + pyrite + sphalerite (stage 1), followed by relatively coarse-grained Mn–Fe carbonate + Fe-rich sphalerite + galena + pyrite (stage 2). The second phase was marked by assemblages of quartz + pyrite + Fe-poor sphalerite and Ag-rich galena + tetrahedrite + sericite (stage 3), quartz + Sb–Pb sulfosalt minerals mainly composed of boulangerite and jamesonite (stage 4), quartz + stibnite ± cinnabar (stage 5), and quartz ± calcite (stage 6). Sulfides of stage 2 have δ34SV–CDT of 8.4–12.0‰, 206Pb/204Pb ratios of 19.648 to 19.659, 207Pb/204Pb ratios of 15.788 to 15.812, and 208Pb/204Pb ratios of 40.035 to 40.153. Sulfides of stage 3 have similar δ34SV–CDT of 6.1–11.2‰ and relatively more radiogenic lead isotopes (206Pb/204Pb = 19.683–19.792). Stage 4 Sb–Pb sulfosalt minerals have δ34SV–CDT of 5.0–7.2‰ and even more radiogenic lead (206Pb/204Pb = 19.811–19.981). By contrast, stibnite of stage 5 has δ34SV–CDT of 4.5–7.8‰ and less radiogenic lead (206Pb/204Pb = 18.880–18.974). Taken together with the geological observations that the Pb–Zn-bearing Mn–Fe carbonate veins were crosscut by various types of quartz veins, sphalerite and galena of stage 2 underwent dissolution and remobilization, and that Sb–Pb(−Fe) sulfosalts formed at the expense of Pb from stage 2 galena and of Fe from stage 2 sphalerite, we argue that the early Pb–Zn veins were overprinted by later Sb-rich fluids. Stage 2 fluids were likely acidic and oxidized and leached lead from high-grade metamorphic rocks of the Greater Himalayan crystalline complex (GHC) and sulfur from reduced rocks, such as slate of the Ridang Formation, along N–S trending faults, leading to precipitation of Pb–Zn sulfides and Mn–Fe carbonate and formation of solution collapse breccias. Later Sb-rich fluids leached Pb from the GHC and the pre-existing sulfides and deposited Fe-poor sphalerite, Ag-rich galena, tetrahedrite, Sb–Pb sulfosalts, and stibnite in quartz veins that cut pre-existing Pb–Zn-bearing Mn–Fe carbonate veins. The Sb-rich fluids also likely leached Pb from Early Cretaceous gabbro and formed stibnite at shallow levels where early Pb-Zn-bearing Mn-Fe carbonate veins are absent. A sericite 40Ar–39Ar plateau age of 17.9 ± 0.5 Ma from stage 3 veins represents the timing of the onset of stage 3 mineralization. [ABSTRACT FROM AUTHOR]

Zhaxikang is one large Sb–Pb–Zn–Ag deposit located in the North Himalaya of southern Tibet. To date, the genesis of this deposit still remains controversial. Here, we present new pyrite Fe and sphalerite Zn isotopic data for the first three stages of mineralization, Fe–Zn isotopic data for Mn–Fe carbonate that formed during the first two stages of mineralization, and Zn isotopic data for the slate wall rocks of the Jurassic Ridang Formation to discuss the genesis of the Zhaxikang deposit. The overall δ 56 Fe and δ 66 Zn values range from −0.80‰ to 0.43‰ and from −0.03‰ to 0.38‰, respectively. The δ 56 Fe values of Mn–Fe carbonates are lighter than those of associated pyrite in six mineral pairs, indicating that the iron carbonates are preferentially enriched in light Fe isotopes relative to pyrite. The sphalerite has lighter δ 66 Zn values than associated Mn–Fe carbonates in three mineral pairs. The δ 56 Fe values of pyrite that formed during the first three stages of mineralization gradually increase from stage 1 (−0.33‰ to −0.09‰) through stage 2 (−0.30‰ to 0.19‰) to stage 3 (0.16‰–0.43‰). In comparison, the sphalerite that formed during these stages has δ 66 Zn values that gradually decrease from stage 1 (0.16‰–0.35‰) through stage 2 (0.09‰–0.23‰) to stage 3 (−0.03‰ to 0.22‰). These data, in conjunction with the observations of hand specimens and thin sections, suggest that the deposit was overprinted by a second pulse of mineralization. This overprint would account for these Fe–Zn isotopic variations as well as the kinetic Rayleigh fractionation that occurred during mineralization. The temporally increasing δ 56 Fe and decreasing δ 66 Zn values recorded in the deposit are also coincident with an increase in alteration, again supporting the existence of two pulses of mineralization. The δ 56 Fe values of the first pulse of ore-forming fluid were calculated using theoretical equations, yielding values of −0.54‰ to −0.34‰ that overlap with those of submarine hydrothermal solutions (−1‰ to 0‰). However, the δ 56 Fe values of the stage 3 pyrite are heavier than those of typical submarine hydrothermal solutions, which suggests that the second pulse of mineralization was probably derived from a magmatic hydrothermal fluid. In addition, the second pulse of ore-forming fluid has brought some Fe and taken away parts of Zn, which results the lighter δ 66 Zn values of sphalerite and heavier δ 56 Fe values of pyrite from the second pulse of mineralization. Overall, the Zhaxikang deposit records two pulses of mineralization, and the overprint by the second pulse of mineralization causes the lighter δ 66 Zn values and heavier δ 56 Fe values of modified samples. [ABSTRACT FROM AUTHOR]

Porphyry systems are known to form in magmatic arc environment and commonly include porphyry Cu, epithermal Pb–Zn–Au–Ag, skarn polymetallic mineralization, etc. The systems are rarely reported in collisional zones, such as the Gangdese belt in southern Tibet where many postcollisional porphyry copper deposits occurred. In addition, other types of mineral systems are rarely present except porphyry copper mineralization in the Gangdese belt. In this study, we present Pb–Zn-bearing quartz veins at Luobuzhen in the western Gangdese belt. The Luobuzhen Pb–Zn veins cross-cut dacite of the Linzizong Group with zircon U–Pb age of 50.1 ± 0.2 Ma and monzogranite with zircon U–Pb age of 17.1 ± 0.1 Ma. Ore minerals include sphalerite, galena, chalcopyrite, and pyrite; gangue minerals are quartz with minor chlorite and sericite. Primary fluid inclusions of quartz are liquid-rich, aqueous, and two-phase inclusions. The homogenization temperatures of these primary inclusions are moderate to high (267–400 °C), and salinities range from 8.9 to 18.4 wt.% NaCl equiv. Quartz has δ 18 O SMOW values of 6.2–9.3‰, while sulfides have δ 34 S V-CDT values of −5.1‰ to 0.1‰, 206 Pb/ 204 Pb of 18.722–18.849, 207 Pb/ 204 Pb of 15.640–15.785, and 208 Pb/ 204 Pb of 39.068–39.560. These data suggest that magmatic fluids with contribution from meteoric water, magmatic sulfur, and lead derived from upper crust and metasomatized mantle by Indian continental materials would be critical for the Luobuzhen base metal mineralization. The Dongshibu area, located at ∼2 km east of the Luobuzhen, is characterized by high concentrations of Cu (up to 1450 ppm) and Mo (up to 130 ppm) of stream sediments, which is quite different from high concentrations in Pb, Zn, Ag, and Au shown in the Luobuzhen area. In addition, porphyry copper mineralization-related alteration and veins/veinlets occur in the Miocene monzogranite at Dongshibu. The monzogranite is characterized by high Sr/Y ratios, which are also shown on ore-forming intrusions in the Gangdese postcollisional porphyry copper deposits, and shows similar zircon Hf isotopes to the ore-related high Sr/Y intrusions from the Zhunuo porphyry copper deposit which is located ∼20 km northeast of the Luobuzhen-Dongshibu. A comprehensive analysis allows us to infer that the base metal veins at Luobuzhen are components of a porphyry Cu system with porphyry Cu mineralization likely present at Dongshibu and epithermal Au–Ag veins possibly occurring at Luobuzhen, which are indicative of the existence of porphyry copper systems in collisional zones. The potential porphyry Cu mineralization and epithermal Au–Ag veins should be targeted in future exploration at Luobuzhen-Dongshibu. [ABSTRACT FROM AUTHOR]

The Gangdese is a newly explored porphyry copper ore belt in China. Except for the Cu (± Mo ± Au) porphyry deposits there are some Mo (± Cu ± W) porphyry and skarn deposits in this belt. Two pulses of molybdenite mineralization are recognized in the central Lhasa subterrane with ancient continent crust, including the Paleocene–Eocene (65–52 Ma) porphyry Mo and skarn Mo–W deposits formed during the rollback of Neo-Tethyan oceanic slab in collisional setting, and Miocene (21–15 Ma) porphyry Mo–Cu deposits generated in the postcollisional setting. The Gangdese copper deposits also occur during these two periods but are distributed in the southern Lhasa subterrane dominated by juvenile crust through mantle-derived magmatism resulting from Neo-Tethyan ocean lithosphere subduction. The intrusions related to molybdenite mineralization have relatively lower bulk-rock ε Nd (t) and higher ( 87 Sr/ 86 Sr) i values, lower zircon ε Hf (t) values and older Hf model ages, lower molybdenite Re contents, and more radiogenic Pb isotopes than the coeval copper related porphyries in the Gangdese belt. In addition, the Miocene Mo–Cu related intrusions generally have lower zircon Ce 4 + /Ce 3 + ratios than the Miocene Cu (± Mo) related intrusions. These data indicate that more contributions from mature continental crustal materials play crucial role in the generation of Mo than Cu porphyry mineralization in the Gangdese belt. The Eocene Mo related intrusions are characterized by high SiO 2 (68–76%) and K 2 O (5.1–5.9%) concentrations, enrichment of large-ion lithophile elements (LILE), depletion of high field strength elements (HFSE), and low Sr/Y (7.5–23.8) ratios. Their Sr–Nd isotope compositions (ε Nd (t) = − 3.4 to − 4.6; 87 Sr/ 86 Sr (i) = 0.70622–0.70679) indicate that they are associated with partial melting of mantle wedge mixing with significant amounts (55%–65%) of middle-upper crustal materials. The Miocene Mo–Cu related intrusions have relatively high SiO 2 (64%–73%) and K 2 O (1.9–4.8%) contents and are characterized by enrichment of LILE, depletion of HFSE, and high Sr/Y ratios (55–189). Their Sr–Nd isotope compositions (ε Nd (t) = − 4.6 to − 3.4; 87 Sr/ 86 Sr (i) = 0.70622–0.70679) are indicative of derivation from remelting of previously subduction modified Tibetan lithosphere with significant amounts (50%–70%) of middle-upper crustal materials. For the Gangdese Mo (± Cu) porphyry mineralization, Mo metal was suggested to be derived from the middle–upper crustal materials, particularly the Carbonaceous–Permian marine sedimentary, whereas Cu metal to be sourced from the Gangdese Miocene Cu fertile magmas. The exploration targeting of the Gangdese molybdenite deposits should be focused on southern part of the central Lhasa subterrane where the Carbonaceous–Permian strata occur. The occurrence of Mo–Cu porphyry deposits could provide clue for targeting Cu–Mo porphyry deposits in the Gangdese belt. The Gangdese molybdenite deposits share many similarities with the East Qinling molybdenite deposits, such as type of ore deposits, geodynamic setting of their formation, variable Mo grades and high F contents. [ABSTRACT FROM AUTHOR]

The North Himalaya is a prospective area for Sb, Sb–Au, Au, Pb–Zn(− Ag), and Sb–Pb–Zn–Ag mineralization. Geochemical anomalies for mineralizing elements and element associations were identified using concentration–area (C–A) fractal model together with statistical analyses, including the mean ± 2 standard deviation (Mean + 2STD) and the median ± 2 median absolute deviation (Median + 2MAD). The results show that the Mean + 2STD for log-transformed data and C–A model could well identify the geochemical anomalies associated with mineralization in the North Himalaya. Sb + Au anomalies show a better spatial association with Sb, Sb–Au, and Sb–Pb–Zn–Ag deposits than those of single Sb element. Au anomalies are associated with all deposits, and Pb + Zn + Ag anomalies are associated with Pb–Zn and Sb–Pb–Zn–Ag deposits. In addition, weak anomalies associated with Sb mineralization can be identified by the singularity method. With the utilization of the Sb + Au, Sb, Au and Pb + Zn + Ag anomalies identified by C–A fractal model and Mean + 2STD for log-transformed data, as well as the singularity method, we can facilitate the exploration targeting of various deposits in the North Himalaya. In addition, our results also show that principal component analysis (PCA) of centered logratio (clr) transformed data can accurately recognize three different geochemical assemblage compositions representing three different types of mineralization (i.e., Au, Pb–Zn–Ag and Sb) in the North Himalaya. [ABSTRACT FROM AUTHOR]

Giant (e.g., Qulong and Jiama) and large (e.g., Chongjiang, Tinggong, and Dabu) porphyry Cu±Mo±Au deposits in the eastern part of the Gangdese belt, southern Tibet have high Cu concentrations (120–7116ppm), while large Zhunuo porphyry Cu deposit in the western part of the belt have low Cu concentrations (<40ppm) in the small-scale (about 1 sample per 16km2) stream sediment geochemical data. Many statistical methods including [mean±2standard deviation (Std)], [median±2median absolute deviation (MAD)], boxplot and factor analysis were applied to delineate the anomaly, showing that there is marked Au and no Cu concentration anomaly in the Zhunuo area. Composite analysis indicates that this strong Au concentration anomaly in the Zhunuo area relates to Cu mineralization which was demonstrated by the large-scale (about 1 sample per 1km2) stream sediment data. The absence of Cu concentration anomaly in the Zhunuo area is due to the low sampling density. Our recent analysis of these small-scale stream sediment data using the local singularity method indicates that there is one weak Cu singularity anomaly in the Zhunuo area. However, the local singularity method seems to be unsuitable to the small-scale stream sediment data and not good for targeting further investigation since values of α-Cu<2 almost occupy 70% of the total data. We hope that our results will not only raise awareness of reanalyzing those anomalies without characteristics of high element concentrations, large size, and marked coincidence of element assemblages (HLCAs) but also be useful for evaluation of prospecting potential in areas where only small-scale steam sediment survey was conducted. [ABSTRACT FROM AUTHOR]

[Display omitted] • Gangdese Miocene fertile and barren adakite-like intrusions share similar ΔFMQ values and apatite S concentrations. • Variations of apatite Cl and S concentrations from core to rim indicate fluid exsolution in fertile and barren rocks. • Some barren porphyries have higher apatite/melt Cl concentrations than the fertile intrusions. • Enrichment of melt Cl and S alone is not critical to forming economic porphyry copper mineralization. • Caution must be taken when applying compositions of detrital zircon and apatite grains to ore prospecting. Gangdese porphyry copper belt in southern Tibet of China contains many Miocene fertile and barren adakite-like intrusions. Their magmatic oxidation state and volatile concentrations were poorly constrained. Here, we present apatite and zircon composition data for the Miocene fertile intrusions in the Qulong, Jiru, and Zhunuo porphyry copper deposits, and the coeval barren porphyries at Yare, Mayum, and Lasa in the Gangdese belt. Magmatic zircons of intrusions from the six locations share similar ΔFMQ (FMQ represents the reference buffer fayalite + magnetite + quartz) values, indicating both fertile and barren rocks have similar magmatic oxidation state. Variations of apatite Cl concentrations and characteristics of S- and Cl-rich core to abruptly S- and Cl-poor rim at Qulong, Jiru, Zhunuo, Yare, and Mayum are indicative of fluid exsolution from vapor-saturated magma. In contrast, fluid exsolution was not recognized from the available apatite composition data at Lasa which are characterized by constant or increasing apatite Cl concentrations with decreasing F/Cl ratios from core to rim. Some apatites at Lasa have high SO 3 concentrations at the core compared with the rim, which would be attributed to early crystallization from S-rich magma followed by crystallization of sulfate minerals in a vapor-undersaturated magma. Some apatites from the fertile intrusions at Qulong, Jiru, and Zhunuo have lower Cl concentrations than those from the barren rocks at Yare, Mayum, and Lasa, which is consistent with the observation from the calculated melt Cl concentration. In addition, the SO 3 concentrations at the core of apatites from all the fertile rocks are overlapping with those from all the barren rocks. Therefore, enrichment of Cl and S alone in melts may not be critical to forming economic porphyry copper mineralization in the Gangdese belt. Cautions must be taken when using compositions of detrital zircon and apatite grains to evaluate metallogenic potential during regional geochemical surveys. [ABSTRACT FROM AUTHOR]

[Display omitted] • Eocene and Miocene rapid cooling and exhumation occurred at Zhunuo. • Missing portion of orebody in the eastern part of Zhunuo would have been eroded. • Gangdese Miocene porphyry copper deposits may share similar cooling and exhumation history during Miocene. Gangdese of southern Tibet is the largest porphyry copper belt in China. Although ore-forming processes have been extensively concerned, the post-mineralization ore preservation state was poorly focused on. Here, we reported apatite fission track (AFT) data for three porphyry copper deposits in the belt (Zhunuo, Jiru and Dabu) to reveal the cooling and exhumation history and evaluate ore preservation. The AFT ages are of 13.5 ± 2.2 to 9.4 ± 1.2 Ma (2σ) for the Miocene monzogranite and granite porphyry, 5.9 ± 1.4 to 3.5 ± 0.8 Ma (2σ) for the Eocene quartz porphyry and rhyolite, and 32.6 ± 8.8 Ma (2σ) for the Eocene rhyolite at Zhunuo. Combined with the thermal history modelling results, these AFT ages and the elevations of samples revealed two rapid cooling episodes at ~10 Ma and ~4 Ma, respectively, in the Zhunuo deposit. Available AFT data from both sides of a nearly N-trending fault at Zhunuo indicated the eastern part would likely have been uplifted relative to the western part where orebodies occurred. The missing portion of orebodies in the eastern part should be located at ca. 600–1200 m above the present surface, all or part of the displaced orebodies would have been eroded at Zhunuo. Our new AFT ages at Jiru (15.4 ± 3.4 to 8.4 ± 1.4 Ma; 2σ) and Dabu (16.4 ± 2.4 to 11.9 ± 3.4 Ma; 2σ), together with the previous low-temperature geochronological data, indicated that Gangdese porphyry copper belt may have undergone similar cooling and exhumation history during ~15–10 Ma. [ABSTRACT FROM AUTHOR]

• Early- and late-stage pyrite have high concentrations of Au and As at Bangbu. • Sulfur for mineralization was derived from the Greater Himalayan crystalline complex. • Bangbu deposit occurred during or after amphibolite-facies metamorphism during ~50–45 Ma. The Bangbu orogenic gold deposit in the North Himalaya of the southern Tibet contains more than 40 t Au at an average grade of 7.0 g/t. In this deposits, gold-bearing quartz veins were controlled by nearly E-trending Qusong-Cuogu-Zhemulang shear zone and occurred within the secondary faults which crosscut Late Triassic greenschist- facies rocks. To further understand the sulfur source and ore-forming process, we have conducted a compressive study of in-situ SIMS sulfur isotopes and LA-ICP-MS trace element compositions of two stages of pyrite at Bangbu. Early-stage pyrite (Py1) is coarse-grained (mostly 0.2–2 mm) and euhedral, and has gold concentrations of less than 0.3–54 ppm (mean of 20 ppm) and δ34S values of 1.6–5.1‰ (mean of 3.2‰). Late-stage pyrite (Py2) is generally fine-grained (mostly <50 μm to 1 mm) and subhedral to anhedral, and has gold concentrations of 3.6–115 ppm (mean of 30 ppm) and δ34S values of 0.9–5.2‰ (mean of 2.7‰). Gold occurs mainly as invisible refractory within Py1 and Py2, and to a lesser extent as native gold within quartz, pyrite, arsenopyrite and sphalerite. Sulfur for Bangbu gold mineralization was probably sourced from the Greater Himalayan crystalline complex. Release of ore-forming fluids was likely related to amphibolite-facies metamorphism during ~50–45 Ma. Ore fluids deposited Au-rich pyrite during early and late mineralization stage and precipitation of native gold was probably related to fluid boiling and/or remobilization of invisible gold within pyrite. [ABSTRACT FROM AUTHOR]

The Zhibula Cu skarn deposit contains 0.32 Mt. Cu metal with an average grade of 1.64% and is located in the Gangdese porphyry copper belt in southern Tibet. The deposit is a typical metasomatic skarn that is related to the interaction of magmatic–hydrothermal fluids and calcareous host rock. Stratiform skarn orebodies occur at the contact between tuff and marble in the Lower Jurassic Yeba Formation. Alteration zones generally grade from a fresh tuff to a garnet-bearing tuff, a garnet pyroxene skarn, and finally to a wollastonite marble. Minor endoskarn alteration zonations are also observed in the causative intrusion, which grade from a fresh granodiorite to a weakly chlorite-altered granodiorite, a green diopside-bearing granodiorite, and to a dark red-brown garnet-bearing granodiorite. Prograde minerals, which were identified by electron probe microanalysis include andradite–grossularite of various colors (e.g., red, green, and yellow) and green diopside. Retrograde metamorphic minerals overprint the prograde skarn, and are mainly composed of epidote, quartz, and chlorite. The ore minerals consist of chalcopyrite and bornite, followed by magnetite, molybdenite, pyrite, pyrrhotite, galena, and sphalerite. Three types of fluid inclusions are recognized in the Zhibula deposit, including liquid-rich two-phase inclusions (type L), vapor-rich two-phase inclusions (type V), and daughter mineral-bearing three-phase inclusions (type S). As the skarn formation evolved from prograde (stage I) to early retrograde (stage II) and later retrograde (stage III), the ore-forming fluids correspondingly evolved from high temperature (405–667 °C), high salinity (up to 44.0 wt.% NaCl equiv.), and high pressure (500–600 bar) to low-moderate temperature (194–420 °C), moderate-high salinity (10.1–18.3 and 30.0–44.2 wt.% NaCl equiv.), and low-moderate pressure (250–350 bar). Isotopic data of δ 34 S (− 0.1‰ to − 6.8‰, estimated δ 34 S fluids = − 0.7‰), δD H2O (− 91‰ to − 159‰), and δ 18 O H2O (1.5‰ to 9.2‰) suggest that the ore-forming fluid and material came from magmatic–hydrothermal fluids that were associated with Miocene Zhibula intrusions. Fluid immiscibility likely occurred at the stage I and stage II during the formation of the skarn and mineralization. Fluid boiling occurred during the stage III, which is the most important Cu deposition mechanism for the Zhibula deposit. [ABSTRACT FROM AUTHOR]

The Zhibula Cu skarn deposit (19.5 Mt ore @ 1.64%), near the Qulong porphyry Cu–Mo deposit, is located in the Gangdese porphyry copper belt in southern Tibet. The deposit is a typical metasomatic skarn that is related to the interaction of magmatic-hydrothermal fluids and calcareous host rocks. Stratiform skarn orebodies are mainly distributed in the contact between tuff and marble in the lower part of the Jurassic Yeba Formation. Endoskarn zonations for an outward trend are observed in the granodiorite, which grade from a fresh granodiorite to a weakly chlorite-altered granodiorite, a green diopside-bearing granodiorite, and a dark red-brown garnet-bearing granodiorite. The Zhibula granodiorite and monzogranite have similar secondary ion mass spectrometry (SIMS) zircon U–Pb ages of 16.9 ± 0.3 Ma and 17.0 ± 0.2 Ma, respectively. They exhibit different fractional crystallization from granodiorite (SiO 2 = 64.8–69.3 wt.%) to monzogranite (SiO 2 = 72.3–76.8 wt.%). Both the granodiorite and monzogranite are characterized by high Al 2 O 3 (12.6–16.7 wt.%) and K 2 O (1.5–5.5 wt.%) contents, high Sr/Y (35–151) and La/Yb (19–48) ratios, and variable MgO (0.16–3.91) and Mg# (31–61) values. They display features of enrichment in large ion lithophile elements (LILEs, e.g., Rb, Ba, Sr, and K), depletion in high field strength elements (HFSEs, e.g., Nb, Ta, Ti, and P), and moderate negative Eu anomalies (δEu = 0.58–0.98). They show restricted in situ zircon Hf isotopic compositions (+6.7 to +8.8; only one sample is +4.5) and consistent δ 18 O values (+6.0‰ to +6.6‰). The geochemical data indicated that the Miocene Zhibula granitic intrusions formed by the magma that were characterized by high Sr/Y ratios and were derived from the partial melting of the thickened juvenile lower crust, which may have been metasomatized by the slab melts during subduction of the Neo-Tethyan oceanic crust and were induced by the convective removal of the thickened lithosphere. In addition, the Zhibula Cu skarn deposit and the Qulong Cu–Mo deposit form a significant porphyry–skarn ore system. [ABSTRACT FROM AUTHOR]

Processes generating fertile magma and associated porphyry Cu deposits in post-collision tectonic settings remain uncertain. Dabu, located in the Gangdese porphyry Cu belt of southern Tibet, is a typical porphyry Cu–Mo deposit that formed in a post-collision setting. The deposit records two stages of magmatism: an Eocene (46 ± 1 Ma) barren monzogranite (EG); and a fertile Miocene (15 ± 1 Ma) monzogranite porphyry (MMP). These intrusions have similar Sr–Nd ( 87 Sr/ 86 Sr (i) = 0.70514 to 0.70573, εNd(t) = − 2.78 to + 0.77) and zircon Hf (εHf(t) = + 3.46 to + 8.85) isotopic compositions that fall within the range of the Palaeocene–Eocene Gangdese Batholith and the coeval Linzizong volcanics and plot on a mixing line between Tethyan basalts and Indian Ocean pelagic sediments. These features, coupled with the variable Sr/Nd, Sr/Th, Ba/Th, and Rb/Y ratios of the intrusions, are indicative of a common source involving basaltic lower crustal melts underplated during the Palaeocene and Eocene. The basaltic material was sourced from a mantle wedge that was metasomatized by Neo-Tethyan slab-derived fluids and oceanic sediments. The MMP, however, formed under a higher magmatic oxygen fugacity than did the EG, as indicated by their higher zircon Ce 4 + /Ce 3 + ratios (87-1112) and higher f O 2 values (ΔFMQ = 5), determined using ilmenite–magnetite mineral pairs. The decompression and discharge of SO 2 during the Linzizong volcanic event and the fractionation of magnetite could account for the low oxygen fugacity (Ce 4 + /Ce 3 + = 58–164; ΔFMQ = − 0.3) of the EG as well the limited development of porphyry deposits associated with the Gangdese Batholith. The MMP and Miocene mineralization-related intrusions within other Gangdese porphyry Cu deposits have high Sr/Y and V/Sc ratios and a negative correlation between Dy/Yb and SiO 2 , all of which are indicative of the crystallization of hornblende from a hydrous mafic melt. The EG and Gangdese Batholith, however, have low Sr/Y and V/Sc ratios and decreasing Sr concentrations over a wide range of SiO 2 contents, indicating that these intrusions formed from dry melts that had undergone significant plagioclase fractionation. Late-crystallized hornblende is generally present as small crystals within early formed feldspar phenocrysts in the EG, which is in good agreement with a rapid increase followed by a decrease in Y and Dy concentrations at ~ 60 wt.% SiO 2 . In addition, apatite in MMP has F (2.66–3.72%) and Cl (0.06–0.53%) volatile contents that are higher than those of apatite from EG (0.85–1.50% F and 0.02–0.03% Cl). These geochemical and mineralogical characteristics suggest that EG formed from a relatively dry magma with < 4.0% H 2 O, whereas MMP formed from a more hydrous magma with > 5.5% H 2 O. It is here proposed that long-lived subduction caused the high oxygen fugacity conditions of the arc magma by adding oxidized components to the sub-arc mantle in addition to F, Cl, S, and Cu. Long-term metamorphic dehydration resulted from the India–Asia collision, and subsequent crust thickening and shortening was responsible for the high water contents by continuously replenishing the basaltic melts at the base of the lower crust. Both subduction-related metasomatism and late-collision-related metamorphic dehydration controlled the genesis of fertile magma that formed the post-collision porphyry Cu–Mo deposits of southern Tibet. [ABSTRACT FROM AUTHOR]

Geochemical exploration data plays a vital role in mineral prospectivity mapping (MPM) for discovering unknown mineral deposits. In this study, compositional balance analysis (CoBA), unsupervised and supervised learning are collaboratively used to improve the practice of identification of geochemical anomalies related to mineralization in the Qulong-Jiama mining district of Tibet. For CoBA, five balances of geochemical elements were constructed by the sequential binary partition (SBP) technique, facilitating the interpretation of geochemical/geological processes and contrasting with geochemical anomalies generated by unsupervised and supervised learning. The iterative self-organizing data analysis techniques algorithm (ISODATA) and isolation forest (iForest) are used for preprocessing the geochemical data and therefore optimizing the appropriate training sets (e.g., positive and negative training samples) for supervised learning. Different training datasets including locations of known mineralization, randomly selected positive samples from resulting clusters by ISODATA and outliers by iForest are fed to the support vector machine (SVM) and random forests (RF) algorithm. The results of high AUC values indicate that supervised learning can effectively delineate prospective areas both with SVM and RF, however, the excessive large area of high-prospectivity and a bias toward known mineralization makes the outcomes of MPM unpractical. Nevertheless, a hybrid of the CoBA, unsupervised learning and supervised learning could alleviate such situations and provide insights into MPM using the geochemical data. • Detection of geochemical anomalies related to mineralization using a hybrid method • The effects of training datasets on mineral prospectivity mapping • The paper provides new insights into mineral exploration using geochemical data. [ABSTRACT FROM AUTHOR]

This paper reviews the spatial-temporal distribution, geological and geochemical features, and geophysical context of diverse types of Cenozoic ore deposits formed during India-Eurasia continental collision in Tibet, in order to shed new light on their genesis and their control by mantle lithosphere. The parental magmas for porphyry-skarn Cu (± Mo ± Au) deposits were derived from metal-rich pre-Cenozoic juvenile crust, and the high magma oxidation state was controlled by involved mantle-derived basic magmas and thickened crust condition; magma emplacement was controlled by structures related both to tears in the subducting continental slab to deep and to mantle-crust decoupling parts at depth. Orogenic Au deposits mostly formed intermittently from hydrothermal fluids formed by devolatilization of earlier-fertilized mantle lithosphere that was triggered by asthenosphere upwelling; they were largely controlled by lithosphere-scale shear systems that reactivated earlier-formed suture zones. Giant MVT Zn Pb deposits, hosted by ancient oil reservoirs, formed during salt diapirism and infiltration of metal-rich basinal brines related to crustal-scale channel flow. The diverse range of ore deposits was derived predominantly through release of metal and fluid components, introduced into the crust and mantle lithosphere that occurred in the earlier oceanic subduction during anomalous lithosphere-scale deformation. The metallogenic history of collisional orogens contrasts with those of accretionary orogens. • Tibetan mineralization system provides an important global insight into metallogenesis during continental collision. • Lithosphere architecture and fertility formed by oceanic subduction control diverse ore deposits in collision setting. • Diverse types of Tibetan ore deposits have different genesis to those from oceanic subduction settings. • Tibetan ore deposits formed in various geodynamic settings of thrusting, shearing, rotation, and rifting. [ABSTRACT FROM AUTHOR]

[Display omitted] • K-feldspar granite porphyry is the causative rock at the 41 Ma Yulong porphyry Cu deposit. • Porphyry deposits have causative magma with ΔFMQ≈1.0~2.5, 4~6 wt% H 2 O, 40~120 ppm Cu and 10~100 ppm S. • Economic porphyries have shallower emplacement depth and larger magma volume than barren ones. • Anticline and carbonate wall rocks trigger mineralization at Yulong rather than nearby intrusions. The relative importance of the oxidation state, water content, and copper and sulfur content of the causative magma in the formation of porphyry Cu deposits is hotly debated. The giant Yulong Cu deposit in Eastern Tibet, with proven reserves of 6.5 Mt Cu at 0.62%, is an example of an economically important porphyry deposit. We investigate the relative roles of factors and different processes controlling the formation of the ores. Zircon U-Pb age data and whole rock, amphibole and apatite major and trace element geochemistry are reported together with previously published data. The results indicate a focused sub-alkaline magma event at 41 Ma in the North Yulong district and contemporaneous mineralization between 41.0 and 40.9 Ma at Yulong. Among the Yulong intrusive complex, the causative K-feldspar granite porphyry with high K 2 O (up to 7 wt%) and SiO 2 (∼70 wt%) contents and elevated Sr/Y ratios (70–90), is interpreted to be a product of fractional crystallization of the evolved sub-alkaline magma. When the Yulong deposit is compared with the global porphyry Cu deposits with similar metal endowment and coeval sub-economic intrusions and barren igneous rocks in the belt, we find that high oxidation states (ΔFMQ + 1.0∼+2.5) and water contents (∼4–6 wt%) coupled with elevated background Cu contents (∼40–120 ppm) in the causative magma are essential in the formation of porphyry Cu deposits. However, the porphyry Cu deposits have magmatic S concentrations (∼10–100 ppm; estimated from apatite SO 3 contents) comparable to that of the barren igneous rocks, independent of the relative timing of apatite crystallization to fluid exsolution. Overall, these conditions are necessary but not sufficient alone to form a porphyry deposit. The economic porphyries commonly have shallower emplacement depths (∼4–5 km) which favor extensive fluid exsolution and larger magma volume (∼50–250 km3 at Yulong) which provide enough storage of ore elements than the barren igneous rocks. In the North Yulong district, extensive fluid exsolution is absent from the two sub-economic intrusions indicated by their relatively high and fixed oxygen fugacity and H 2 O and Cl contents in the magma evolution. In contrast, at Yulong, a local anticlinal structure provided a trap in which exsolved fluid from the magma was concentrated, and carbonate wall rocks triggered the efficient precipitation of metals during intense fluid-rock interactions and skarn alteration. Both are also critical processes in the formation of the giant Yulong Cu deposit. [ABSTRACT FROM AUTHOR]