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Jiang S.Y.,Nanjing University | Sun Y.,Nanjing University | Sun M.Z.,Nanjing University | Bian L.Z.,Nanjing University | And 4 more authors.
Acta Petrologica Sinica | Year: 2010

Based on detailed underground and field observation together with regional structure analysis, this paper discussed the feature and evolution of the reiterative fault system and superimposed mineralization and their relationship in the Jiurui ore concentrated district, Jiangxi Province, China. Three fault systems are described, namely, the Hercynian syn-sedimentary fault system developed along the continental margins, Indosinian folding and fault system, and Late Yanshanian negative inversion fault system. Taking the Wushan copper deposit as an example, we revealed the initiation and development of F 1 fault during the three stages and their controls on mineralization. A three-stage conceptual model is proposed as following. During the first Hercynian stage, extension and rifting occurred along the continental margins and a two sub-stage of syn-sedimentary fault system developed. In the later sub-stage, the tensile fractures combined with the deep-seated fault developed which allow the submarine volcanic eruption and hydrothermal ore-forming fluids ascend to form bedded and massive copper-bearing pyrite orebodies. During the second Indosinian stage, the folding and fault development may have caused reverse movement of the previously deposited sedimentary bedded orebodies. During the thrid stage of Late Yanshanian, development of high angle fold-thrust and regional stress may have caused the fault system transformed from compressive into brittle tensile structures, and formed negative inversion structure. Together with the faulting, magmatic-hydrothermal fluids contributed to formation of new orebodies that were superimposed on previous syn-sedimentary mineralization system.

Xu Y.,Nanjing University | Jiang S.,Nanjing University | Zhu Z.,Nanjing University | Zhou W.,Nanjing University | And 3 more authors.
Acta Petrologica Sinica | Year: 2012

In order to constrain petrogenesis and corresponding mineralization significance, a detailed study on geochronology, mineral chemistry, major and trace elemental and Sr-Nd-Hf isotope geochemistry was performed for the quartz diorite-porphyrite and granodiorite porphyry in the Shanshangwan area of the Jiurui ore district, Jiangxi Province. The biotite phenocrysts of the samples are all eastonite, and their compositions indicate a fO2 lower than HM buffer line. All the plagioclase phenocrysts are andesine and characterized by oscillatory zoning texture. Zircon LA-ICP-MS U-Pb dating suggests emplacement ages of 149. 2 ±2. 7Ma and 148. 5 ± 1. 4 Ma for the two northern dykes (II and III), and 139. 0 ± 1. 3 Ma for the southernmost dyke (I) · Shanshangwan intrusive rocks are characterized by SiO2 and K2O compositions of 58. 8% to 63. 0%, and 1. 9% to 2. 4%, respectively, enrichment in light rare earth elements (LREE) and large ion lithophile elements (LILE), and relative depletion in Nb, Ta, Y and Yb. They show no negative Eu anomalies (Eu/Eu* = 0. 98 ∼ 1. 13, with an average of 1. 05) and no negative Sr anomalies. The initial Sr (( 87Sr/86Sr) s = 0. 7060 ∼0. 7092, with an average of 0. 7074), Nd (εNd(t) = -2. 9 ∼ -2. 0, with an average of -2. 3) and zircon Hf (εHf(t) = -11.8∼2.3, with an average of -1.1) isotopic compositions of the Shanshangwan intrusive rocks and their slightly higher MgO contents (ranging from 2. 0% to 2. 8 % with an average of 2. 5 %), high Mg# value (ranging from 42 to 51 with an average of 48) and high compatible trace element (Cr, Ni and V) contents exhibit that the magma may have experienced intense interaction with mantle. Comprehensive geochemical and Sr-Nd-Hf isotopic data demonstrate that the Shanshangwan intrusive rocks may have originated from partial melting of thickened lower crust delaminated into mantle. In addition, several kinds of alteration minerals and Cu mineralization have already been found within the Shanshangwan intrusions, and the petrogenesis of this district is identical with the other mineralization-related granodiorite porphyries in the Jiurui ore district. Therefore we suggest that the contact zone between carbonate rocks of Ordovician and intrusive rocks, and the interface between carbonate strata of Ordovician and siltstone of Silurian would host high potential to form ore deposits of economic significance.

Xu Y.M.,Nanjing University | Jiang S.Y.,Nanjing University | Jiang S.Y.,Wuhan University | Zhu Z.Y.,Nanjing University | And 5 more authors.
Acta Petrologica Sinica | Year: 2013

The major types of copper polymetallic ore deposit in Jiurui ore district include porphyry, skarn and massive sulfide types. Porphyry and skarn types are typical magmatic-hydrothermal deposits, and the massive sulfide deposits of Jiurui area occurred along the strata near the sandstone and dolomite boundary but also located near intrusive rocks, which shows that magmatic-hydrothermal fluids may have also played a crucial role in the mineralization processes. In Jiurui area, petrographic characters of ore-barren intrusive rocks are almost the same as ore-bearing samples, and parameters to identify between ore-bearing and ore-barren intrusive rocks as well as how these parameters affect mineralization are still unknown. In order to solve above problems, a detailed study on geochronology, major elemental geochemistry and mineral chemistry was performed for the ore-bearing and ore-barren quartz diorite-porphyrite and granodiorite porphyry from the Jiurui ore district, Jiangxi Province. Zircon U-Pb dating results demonstrate that extensive magmatism was coeval and intensive in this area, with emplacement ages of 138.2 ± 1.8Ma to 148.0 ± 1.0 Ma for the ore-bearing intrusive rocks, and 139.0 ± 1.3Ma to 149.6 ±3.0 Ma for the ore-barren intrusive rocks, which are consistent within the error range with each other. The variation ranges of SiO2 and other 9 major oxides are quite similar between ore-bearing and ore-barren intrusive rocks. The average temperatures of ore-bearing and ore-barren intrusive rocks are 769°C and 723°C respectively, which are also not much difference. However, the variation range of the ore-bearing intrusive rocks (580∼915°C) is obviously greater than the ore-barren ones (656-796°C). It is remarkable that the average pressure of ore-barren intrusive rocks (5.7kbar) is evidently greater than the ore-bearing samples (1.4kbar). Therefore, the ore-bearing intrusive rocks from the Jiurui area should have experienced a more distinctive pressure decreasing process, which is quite important to form magmatic aqueous phase and brittle failure for hydrothermal circulation. However, decreasing pressure process of an intrusive rock is not the sufficient condition for mineralization, but a necessary condition. Based on the data from Jiurui area, the mineralization potential is weak when the pressure of intrusive rock exceeds 4kbar. The fO2 of the ore-bearing intrusive rocks has a wider variation range than the ore-barren samples and half of the data are plotted above the HM buffer line, but the fO2 data of the ore-barren samples are all plotted below the HM buffer line, which means that high fO2 (higher than HM buffer line) is beneficial to mineralization in Jiurui ore district.

Jiang S.Y.,Nanjing University | Jiang S.Y.,Wuhan University | Xu Y.M.,Nanjing University | Zhu Z.Y.,Nanjing University | And 4 more authors.
Acta Petrologica Sinica | Year: 2013

Jiurui is one of the most important Cu-Au ore district in the Lower-Middle Yangtze Valley metallogenic belt in China. There are generally two ore-forming stages in this belt, one is the Hercynian syn-sedimentary hydrothermal mineralization stage (mainly Fe-S) and the second stage is the Yanshanian magmatic-hydrothermal stage (mainly Cu-Au-Mo). Based on investigations and studies on regional structures, magmatic rocks, and various types of mineralization in the Jiurui district, we summarized the main features of structure, magmatism and mineralization in the Jiurui district. There are two main fault structures in the district that controlled the magmatic emplacement and related mineralization, namely, the strike over step thrust zones with NEE (near EW) direction and brittle-ductile character, and the transcurrent fracture fault zones with SN (near SN) direction and tonsil-torsion character. These two groups of the faults constitute a tectonic framework in the region which looks like a Chinese word "well", and they controlled the magmatic rocks and related mineralization. There are various types of magmatic rocks in this district, with the main types of grandiorite porphyry and quartz diorite-porphyry. These rocks were emplaced during the Early-Middle Yanshanian stage of 138 ∼ 148 Ma. These rocks display various shapes, including apophysis, harpolith, sheet, dyke, and stock. The igneous sheets and dykes are distributed along the thrust zones with NEE direction. In particular, they appear along a faulted structure with a special "Y" shape structure. But the stocks were emplaced at the cross place between the NEE direction and SN direction fault, and these rocks have a close relation with the mineralization. In this paper, we emphasized the SN direction tension faults and their controls on emplacement of granitic porphyry and related mineralization. We have identified four groups of fault with the SN direction of tonsil-torsion character in this district. We suggest that it is worth to pay more attention to the cross places between the Songjiawan-Yanjiacun line and the NEE faults for more detailed exploration. The major mineralization types in the Jiurui district include skarn type, porphyry type (including crypto-explosive breccia type), the superimposed stratabound type, and hydrothermal vein type. In a particular ore deposit, it may be a combination of various types of mineralization. For example, the Wushan deposit is a combination of skarn and superimposed stratabound ores, the Chengmenshan ore deposit is a combination of skarn, porphyry and superimposed stratabound ores.

Jiang S.,Nanjing University | Xu Y.,Nanjing University | Zhou W.,Nanjing University | Zhu Z.,Nanjing University | And 3 more authors.
Acta Petrologica Sinica | Year: 2012

Following our previous study on reiterative fault systems and superimposed mineralization in the Jiurui ore district (Jiang et al., 2010), in this study we conducted a thoroughly investigation on a tectonic-hydrothermal siliceous breccia rock which occurs along the NE trending Yangjishan gold mine-Dingjiashan gold mine-Wangfushan belt. Our study indicates that these siliceous breccia rocks are not sedimentary siliceous rocks in Carboniferous strata as previously thought, but belong to a fault-grinding breccia rock. The rock-forming mechanism of the breccia rocks and their relation to mineralization are also discussed in detail in this paper. Generally speaking, the fault-grinding gravel (grain) include all kinds of boudinage, grinding gravel and cataclastic flow grinding gravel, and it is an indication for maturity of fault zoning texture. Under shearing, the faulted rock may have passed stages of rupturing-fracturing- comminution-grinding and to form a great variety of grinding gravels or grains in different size with appropriate roundness and sphericity. These breccia rocks could have been repeatedly aggregated and fractured, and continuously developed to form a grinding gravel and breccia zone. In the Jiurui ore district, we found that these fault-grinding breccia rocks developed along the main NE-trending structure line of the district and extended tens kilometers long. The breccias are highly silicified with Si02 contents > 90%. The quartz includes both cryptocrystalline and crystalline grains. Some of the breccias contain high Fe203 contents, which may indicate presence of primary sulfide ore breccias which have been oxidized to goethite later on. It is likely that these fault rocks were products of Yanshanian tectonic-magmatic-hydrothermal events. In the Chengmenshan and Wushan deposits, we also found various types of pyrite breccias occurring within the Devonian/Carboniferous strata and layer slip fault zone, which may have formed during the Hercynian syn-sedimentary faulting stage. All these different types of breccias composed the ore complex in the district, which show a multiple stage developing feature and superimposed mineralization characteristics. It is also suggested in this paper that the layer slip fault gravel-breccia zones in other sedimentary strata such as the Devonian/Silurian and Silurian/Ordovician at depths are potential mineralization targets that need to pay more attention in future exploration.

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