Taofa Zhou

Petrogenesis of volcanic and intrusive rocks of the Zhuanqiao stage, Luzong Basin, Yangtze metallogenic belt, east China: implications for ore deposition

The Mesozoic Luzong volcanic basin is located in the Lower Yangtze River fault-depression, along the northern margin of the Yangtze Block. Volcanic and plutonic rocks are widely distributed in the basin and are spatially related to Cu, Fe, Au, Pb, and Zn ore deposits. The magmatic rocks are dominated by an alkali-rich shoshonitic suite of volcanics and intrusives, including both a trachybasalt-basaltic trachyandesite-trachyte series and a diorite-monzonite-syenite-alkali feldspar granite series. Volcanic sequences within the Luzong Basin are subdivided into four stages, namely the Longmenyuan, Zhuanqiao, Shuangmiao, and Fushan stages with magmatism occurring between 136 and 124 Ma. Most mineral deposits were formed during the Zhuanqiao stage from about 134 to 131 Ma, during a longer (140–130 Ma) period of transition from compression to extension within the Luzong Basin. Major element concentrations in the Zhuanqiao volcanic rocks range from 53.97 to 62.59 wt.% SiO2, 0.57–0.94 wt.% TiO2, 3.52–6.07 wt.% Na2O, and 3.60–8.66 wt.% K2O. Combined K2O + Na2O totals lie between 7.87 and 12.49 wt.%, and K2O + Na2O/Al2O3 ranges between 0.47 and 0.71. In comparison, the Zhuanqiao intrusions have SiO2 concentrations between 52.19 and 67.70 wt.%, TiO2 between 0.26 and 1.13 wt.%, Na2O between 1.33 and 6.55 wt.%, and K2O between 2.15 and 8.25 wt.%, with K2O + Na2O values ranging from 5.92 to 12.39 wt.% and K2O + Na2O/Al2O3 ratios between 0.37 and 0.75. The Zhuanqiao volcanic rocks have an average ∑REE (rare earth element) content of 223.17 ppm, whereas the average ∑REE of the Zhuanqiao intrusives is 250.06 ppm. Weak negative Eu anomalies (Eu/Eu* between 0.69 and 1.00) characterize the volcanics, whereas a larger range with more significant negative Eu anomalies (Eu/Eu* values of 0.35–0.94) is present in the plutonics. The Zhuanqiao volcanic rocks and plutons have (Nb/Th)PM ratios of 0.05–0.14 and 0.02–0.14 and (La/Sm)PM of 3.33–4.95 and 3.36–7.29, respectively. Initial 87Sr/86Sr and 143Nd/144Nd ratios and ϵSr(t) and ϵNd(t) of the Zhuanqiao volcanic rocks are 0.7059–0.7067, 0.51194–0.51218, 22.0–33.3, and −10.2 to −5.5, respectively; those of the intrusives are 0.7060–0.7082 and 0.51203–0.51214 and 23.3–54.7 and −8.6 to −6.4, respectively. The geochemistry presented here suggests that both volcanic and intrusive Zhuanqiao stage magmatic rocks were cogenetic and were probably derived from an enriched mantle (EM) source, most probably metasomatized mantle relating to the EM type-I (EM-I). The Zhuanqiao stage magmatism apparently was controlled by differentiation and assimilation of crustal material in a high-level magma chamber. Formation of the Zhuanqiao stage magmatic rocks coincided with the formation of much of the Cu and Fe mineralization within the Luzong Basin. This coeval magmatism and mineralization during the Zhuanqiao stage can be subdivided into three differing mineral deposit affinities: magmatism associated with magmato-hydrothermal vein Cu (e.g. the Jingbian, Shimenan, and Chuanshandong deposits), porphyry-hosted Fe (e.g. the Luohe and Nihe deposits), and skarn Fe (e.g. the Longqiao deposit). Combining geological characteristics with variations in SiO2, K2O + Na2O, and MgO enabled the division of the Zhuanqiao stage magmatism in the Luzong Basin into geochemically distinct units associated with these differing styles of mineralization.

Petrogenetic–metallogenetic setting and temporal–spatial framework of the Yueshan district, Anhui Province, east-central China

The Yueshan district is located in the Anqing–Guichi ore deposit area of the Middle–Lower Yangtze Metallogenic Belt. Two groups of intrusive rocks and three main types of ore mineralization occur in this district: diorite plutons (e.g. Yueshan, Zongpu, Wuheng, and Yangshan) and granite plutons (Hongzhen and Dalongshan), Cu–Au–(Fe) skarn deposits (e.g. Anqing, Tiepuling), Cu–Mo–Au–(Pb–Zn) hydrothermal vein-type deposits (Tongniujing), and hydrothermal uranium mineralization (Dalongshan). Detailed geological and geochemical work suggests that the Cu–Au–(Fe) skarn deposits and the Cu–Mo–Au–(Pb–Zn) hydrothermal vein-type deposits have a close spatial and genetic relationship with the dioritic plutons, whereas the hydrothermal uranium mineralization is associated with A-type granite plutons. Based on the highly precise dating of metal deposits and related plutons in the Yueshan district, such as the molybdenite Re–Os, Os–Os dating, 39Ar–40Ar dating of potassium-bearing minerals and quartz, several Rb–Sr isochrons, SHRIMP zircon U–Pb dating + single-grain zircon U–Pb dating, and the SHRIMP zircon U–Pb dating of Hongzhen granite pluton, we suggest that the extensive magmatism and mineralization in the Yueshan district took place in two episodes: (1) the first episode involved the mineralization of both skarn and vein-type hydrothermal deposits, c.a. 136–139 Ma, related to diorite plutons emplaced at 138.7 ± 0.5 Ma; (2) the second episode attended the hydrothermal uranium mineralization at 106.4 ± 2.9 Ma, related to granite intrusive activity at 126.8 ± 1.0 Ma. These two times of Yueshan petrogenetic–metallogenetic development appear to be consistent with a tectonic environment transition from compression to extension.

The Middle-Lower Yangtze Metallogenic Belt

We dedicate this special issue to Professor Yinfo Chang in appreciation of his lifetime contribution to the study of economic geology in China and in celebration of his 80th birthday. Professor Cha...

Petrogenesis and metallogenic implications for the Machang, Huangdaoshan, and Tuncang plutons in eastern Anhui: an integrated age, petrologic, and geochemical study

ABSTRACT The Tuncang–Chuzhou–Machang area (eastern Anhui province) is geologically located in the intersection between the Yangtze block and the Qinling–Dabie orogenic belt. Many Mesozoic plutons outcrop in this district that are Cu–Au prospective but inadequately studied. We report new LA-ICP-MS zircon U–Pb ages, petrologic, and whole rock geochemical data for three representative plutons at Machang, Huangdaoshan, and Tuncang. New dating results suggest that all the Machang (129.3 ± 1.6 Ma), Huangdaoshan (129 ± 1.7 Ma), and Tuncang (130.8 ± 1.9 Ma) plutons were emplaced in the Early Cretaceous, slightly older than other plutons in neighbourhood of the Zhangbaling uplift. The three plutons contain typical low-Mg adakitic affinities, in which the rocks contain SiO2 >56%, Al2O3 ≥15%, Mg# <53, elevated Sr, Ba, Cr, Ni, Sr/Y, and La/Yb, low Y and Yb and no discernible Eu anomaly. Their petrogenesis may have been related to the delamination and partial melting of the lower crust, which is different from the Chuzhou pluton, which was interpreted to have formed by partial melting of the subducted slabs. We suggest that this petrogenetic difference may explain why the pluton at Chuzhou is Cu–Au fertile, whereas those at Machang, Huangdaoshan, and Tuncang are largely barren. It is proposed that adakitic plutons formed by partial melting of the subducted slabs have high metallogenetic potentiality in the area.

Comparison of normalisation methods for non-normal distributed soil geochemical data: a case study from the Tongling metallogenic district, Yangtze belt, Anhui Province, China

Abstract Geochemical data from soils in mineralised areas commonly have skewed and non-normal distributions. As such, raw soil geochemical data cannot be used for direct geostatistical analysis of spatial variability and interpolation without introducing additional uncertainties to any interpretation. The non-normal distributions will influence the robustness and fitting of variograms to the data, and negatively influence the accuracy of any interpolations produced from these data. Therefore, prior to assessment, the dataset must be transformed to ensure that it has a normal distribution. Three transformations, namely the logarithmic, Box–Cox and Johnson transformations, were applied to As, Cd, Hg, Pb and Zn soil geochemical data from the Tongling metallogenic district, part of the Yangtze metallogenic belt, Anhui Province, China. The results of these transformations were analysed to determine the skewness of the data; and, using a Kolmogorov–Smirnov test, how closely the transformed data approximate a normal distribution. A comparison of the differing normalisation approaches indicates that: the logarithmic transformation could not transform the data to approximate a normal distribution; the Box–Cox transformation removed the skewness of the data but the results were still non-normally distributed; and the Johnson transformation proved to be the optimal method, with the results, including outliers, passing the Kolmogorov–Smirnov test. Both the Johnson and Box–Cox transformations also improved the shape of variograms produced from the data. However, compared to Box–Cox, more of the Johnson transformed data fit within 95% confidence intervals for the Kolmogorov–Smirnov test; this improved data distribution means that this transformation should be considered the preferred geostatistical normalisation tool for soil geochemical data. The application of the Johnson transformation to soil geochemical data may improve the robustness of predictive targeting and mineral exploration in areas of known mineralisation that have non-normal spatially variable data.

Genesis of late carboniferous granitoid intrusions in the Dayinsu area, West Junggar, Northwest China: evidence of an arc setting for the western CAOB

ABSTRACT The Dayinsu area is located in the northern part of the West Junggar district near the border between China and Kazakhstan and is an important component of the Central Asian Orogenic Belt (CAOB). The Dayinsu area hosts numerous granitoid plutons in Devonian–Carboniferous volcano–sedimentary strata. The older Laodayinsu and Kubei (345–330 Ma) plutons are located in the west with the younger Bayimuzha and Qianfeng (330–325 Ma) plutons in the east. The whole-rock SiO2 contents of the four granitoid plutons range from 52.22 to 68.42 wt.% and total alkaline contents (K2O + Na2O) range from 4.94 to 9.16 wt.%. The granites are enriched in large ion lithophile elements and light rare earth elements with depletions in Nb, Ta, Ce, Pr, P, and Ti. The plutons are metaluminous with I-type signatures. The geochemistry of the intrusions suggests that they formed in a subduction zone setting, and subsequently underwent fractional crystallization during emplacement, with higher degrees of fractionation in the eastern sector than in the west. Similarities in the geochronology and geochemical characteristics of the granitoid plutons in Dayinsu to those in the Tabei district (west to Dayinsu area) suggest that both districts are part of the Carboniferous Tarbagatay Mountain intrusive event. The early Carboniferous (345–324 Ma) granitoid intrusions in the Tarbagatay Mountain likely formed in an island arc subduction setting during the evolution of the CAOB.

Petrogenesis and timing of emplacement of porphyritic monzonite, dolerite, and basalt associated with the Kuoerzhenkuola Au deposit, Western Junggar, NW China: implications for early Carboniferous tectonic setting and Cu–Au mineralization prospectivity

ABSTRACT The Kuoerzhenkuola epithermal Au deposit is located in the northern part of the West Junggar region of NW China and is underlain by a recently discovered porphyritic monzonite intrusion that contains Cu–Au mineralization. Zircon LA-ICP-MS U–Pb dating of this intrusion yielded an age of 350 ± 4.7 Ma. The porphyritic monzonite is calc-alkaline and is characterized by high concentrations of Sr (583–892 ppm), significant depletions in the heavy rare earth elements (HREE; e.g. Yb = 0.96–2.57 ppm) and Y (10.4–23.3 ppm), and primitive mantle-normalized multi-element variation diagram patterns with positive Sr and Ba and negative Nb and Ti anomalies, all of which indicate that this intrusion is compositionally similar to adakites elsewhere. The composition of the porphyritic monzonite is indicative of the derivation from magmas generated by the melting of young subducted slab material. The area also contains Nb-enriched basalts that are enriched in sodium (Na2O/K2O = 1.20–3.90) and have higher Nb, Zr, TiO2, and P2O5 concentrations and Nb/La and Nb/U ratios than typical arc basalts. The juxtaposition of adakitic rocks, Nb-enriched basalts, and dolerites in this region suggests that the oceanic crust of the expansive oceans within the West Junggar underwent early Carboniferous subduction. Magnetite is widespread throughout the Kuoerzhenkuola Au deposit, as evidenced by the volcanic breccias cemented by late hydrothermal magnetite and pyrite. In addition, the zoned potassic, quartz-sericite alteration, and propylitic and kaolin alteration in the deeper parts of the porphyritic monzonite are similar to those found in porphyry Cu–Au deposits. These findings, coupled with the mineralogy and geochemistry of the alteration associated with the Kuoerzhenkuola Au deposit, suggest that the mineralization in this area is not purely epithermal, with the geology and geochemistry of the porphyritic monzonite in this area suggesting that a porphyry Cu–Au deposit is probably located beneath the Kuoerzhenkuola Au deposit.

Singularity mapping of fracture fills and its relationship to deep concealed orebodies-A case study of the Shaxi porphyry Cu-Au deposit, China

Porphyry Cu-Au type mineralization forms as a result of magmato-hydrothermal activity and involves the migration of hydrothermal fluids through rock fractures, a process that causes the precipitation of fracture-filling minerals with a volume that is much larger than the orebodies themselves. This means that the mineralization-related geochemical anomalies within the minerals that fill these fractures (i.e. fracture fills) can be used to identify areas prospective for deep-seated or otherwise concealed porphyry-type mineralization. This study focuses on the Shaxi deposit, a concealed porphyry Cu-Au deposit located in the Anhui Province, China, and uses singularity techniques to identify and extract geochemical anomalies associated with porphyry Cu-Au-related fracture fills. These data were used to examine the relationships between geochemical anomalies and known deep and concealed mineralization distinguished from unaltered and unmineralized wall-rock material using a concentration–volume (C–V) model in the study area. This analysis indicates that the geochemical anomalies identified in this study are associated with known areas of mineralization in the Shaxi deposit. Areas defined by fracture fills containing anomalous concentrations of Cu only effectively delineate known areas of shallower Cu mineralization, whereas areas with fracture fills containing anomalous concentrations of Au effectively delineate areas containing either Au mineralization and/or deep-seated Cu mineralization. Our study also identified several other targets that have not been explored in the peripheral areas of the Shaxi deposit, some of which should be considered high priority targets for future exploration for concealed orebodies. This indicates that combining singularity mapping with fracture fill geochemical analysis can effectively delineate geochemical anomalies associated with deep-seated or concealed porphyry-type mineralization, an approach that also may well be applicable to exploration for other types of magmato-hydrothermal or hydrothermal mineral deposits.

Characteristics of the Intracontinental Porphyry Deposits in the Middle‐Lower Yangtze River Valley Metallogenic Belt, Eastern China

world’s copper (Cu) and one fifteenth of the world’s gold (Au) (Sillitoe, 2010), with 97% of the giant-large porphyry Cu (Mo-Au) deposits being generated in magmatic arc setting (Richards; 2003; Cooke et al., 2005; Sillitoe, 2010). Nevertheless, recent studies indicate that important porphyry deposits may also be formed in subduction-unrelated environments, e.g., along continental collision-related orogeny and intracontinental setting (Hou et al., 2009; Chen, 2013; Zhou et al., 2011). The Middle-Lower Yangtze Metallogenic Belt (MLYB) is one of the most important Cu-Au-polymetallic metallogenic belts in eastern China, and has been studied extensively in the past (Zhou et al., 2008). Various models have been proposed concerning the regional metallogeny, with major ones including the “porphyrite iron deposit” (NW Group, 1978), “stratabound skarn deposits” (Chang et al., 1991) and the “superimposed metallogenic system” (Zhai et al., 1992; Chang et al., 2012). With the discoveries of large porphyry Cu-Au deposits at Shaxi and Shujiadian in the recent years addition to the previous discovered porphyry deposits such as Chengmenshan and Fengshandong and other deposits, porphyry deposits are becoming more important exploration targets in the MLYB. Their nature and origin are still controversial, and are attributed variably to be the products of intracontinental magmatism (Hou et al., 2009; Chen, 2013; Zhou et al., 2011) or of the subduction of the Paleo-Pacific Plate (Ling et al., 2009, 2011; Liu et al., 2010; Sun et al., 2010; Xie et al., 2012), and recent study are more and more tend to the former point (Chen et al., 2014; Lv et al., 2014; Wang et al., 2014). To further illustrate the differences between the porphyry deposits formed in intracontinental setting and magmatic (continental or island) arc setting, we have chosen typical continental margin arc porphyry deposits, i.e., Bingham Canyon (US) and Bajo de la Alumbrera (Central Andes); island arc porphyry deposits, i.e., Panguna (PNG) and Batu Hijau (Indonesia) to compare with the MLYB porphyry deposits. It is summarized that: 1. Distribution of magmatic (continental or island) arcgenerated porphyry deposits is commonly linear, and is parallel to the orogeny and perpendicular to the subduction zone (Sillitoe, 2010). The MLYB porphyry deposits are distributed along the Yangtze Fault, oblique to the PaleoPacific subduction zone. 2. Magmatic arc-generated porphyry metallogenic systems are commonly preceded by calc-alkaline or alkaline felsic volcanism (Sillitoe, 1973) that occurs ca. 0.5 ‒ 3 Ma prior to the porphyry emplacement, as evidenced at Bingham (Waite et al., 1997), Farallón Negro (Argentina; Sasso and Clark, 1998; Halter et al., 2004), Yerington (Dilles and Wright, 1988; Dilles and Proffett, 1995), Tampakan, Philippines (Rohrlach and Loucks, 2005) and Yanacocha (Longo and Teal, 2005). No coeval (or similar age) volcanism with the porphyry deposits has been documented in the MLYB. 3. Types of wall rocks vary in different deposits, suggesting porphyry Cu deposits are indiscriminative towards their wall rocks. Wall rocks for magmatic arcgenerated porphyry deposits are commonly volcaniclastic rocks, whereas wall rocks for the intracontinental MLYB porphyry deposits contain sandstone (e.g., Shaxi) and carbonates (e.g., Tongshankou). 4. Major metal sulfides in the MLYB include chalcopyrite, pyrrhotite, pyrite,and bornite. Pyrrhotite is closely associated with skarn, and may suggest the reducing nature of the wall rocks (Kósaka and Wakita, 1978; Perelló et al., 2003), in accordance with the formation of magmatic arc-generated porphyry deposits (Sillitoe, 2010). The MLYB porphyry deposits contain the same vein types as typical magmatic arc-generated porphyry deposits, but with different vein type proportion: ZHOU Taofa, WANG Shiwei, FAN Yu, YUAN Feng, ZHANG Dayu and Noel White, 2014. Characteristics of the Intracontinental Porphyry Deposits in the Middle-Lower Yangtze River Valley Metallogenic Belt, Eastern China. Acta Geologica Sinica (English Edition), 88(supp. 2): 667-669.

The Geochemical Identification on Mo-(Cu) and Cu-Mo Bearing Granitoids and Their Significance: Evidences from Chinese Mo-Bearing Intrusions

In recent years, whole-rock geochemistry has been used for tracing the petrogenesis of magmatism (Loucks & Ballard, 2002), however, metallogenic research according to the whole-rock geochemical characteristics of orebearing magmatism has been largely neglected. In this study, after systematically collecting all the published whole-rock geochemical data of Mo mineralization related granitoids in China, we tried to find their discriminative indicators to identify the Mo-Cu and Cu-Mo bearing granitoids, and further understand how these two types of Mo-bearing granitoids form during their evolution process. This study opens a window to research the features and evolution of ore-forming magmatism.