Jiaodong GF - Rushan, Pengjiakuang, Denggezhuang, Jinqingding, Guocheng
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The Rushan, Pengjiakuang, Denggezhuang, Jinqingding and Guocheng gold deposits are located within the Jiaodong Gold Province on the Jiaodong Peninsular of Shandong Province, northern China, north of Rushan City and approximately 500 km south-east of Beijing. This group is approximately 100 km ESE of the main belt of significant deposits in the gold province - see the other Jiaodong Gold Field record that describes these deposits.
The Jiaodong Peninsular is on the southeastern portion of the North China craton, immediately north of the easternmost part of the ultra-high pressure belt that marks the Late Permian to Early Jurassic suture between with the Yangtze craton to the south. It is made up of a sequence that includes the late Archaean (2.94 to 2.67 Ga with 3.0 to 3.4 Ga components) tonalite-trondhjemite-granodiorite and mafic to felsic volcanic and sedimentary rocks all of which have been subjected to amphibolite to granulite facies metamorphism to form the granulite, gneiss, amphibolite and biotite-bearing schists of the Jiaodong Group. These Archaean rocks are unconformably overlain by a Proterozoic sequence comprising:
i). The Paleoproterozoic Jinshan Group, which is composed of a sequence of mainly silty clastics and calcareous-magnesian carbonates with intercalated mafic to ultramafic volcanics which have all been metamorphosed to a suite of mica schist, quartz-feldspar-biotite gneiss, marbles and graphitic rocks.
ii). The Paleoproterozoic Fenzishan Group, comprising fine-grained gneiss, mica-quartz schist, feldspathic quartzite, magnetite-bearing rocks, marble and graphitic rocks that are the result of upper greenschist to amphibolite facies metamorphism of silty clastic sediments, Mg-rich carbonates, and calcareous clastics and pelites.
These two groups were deposited between 2484 and 2381 Ma and metamorphosed during from 2224 to 1847 Ma (Luliang orogeny) and are overlain by,
iii). The Neoproterozoic lower greenschist facies limestones, dolomite, slate and phyllite of the Panglai Group.
All of these rocks have been subjected to multiple stages of granulite- to greenschist-facies metamorphism over the timespan 2945 to 1674 Ma. They are overlain by Mesozoic shales, clastics and volcanics and are intruded by voluminous Mesozoic (Jurassic to Cretaceous) Yanshanian age granitoid intrusives which occupy over 40% of the terrane emplaced in two episodes, 164 to 155 and 130 to 126 Ma, the first of which is largely due to anatectic reactivation of the basement rocks.
Two main stages of deformation have been defined in the Jiaodong gold province during the late Mesozoic, the first of which was dominated by NW-SE oblique compression, producing a series of NNEŠ to NE-trending brittle-ductile shear zones with sinistral oblique reverse movements, followed by a later reactivation, expressed by brittle structures and half-graben basins. These structures are believed to be subsidiary to the major Tan-Lu fault.
The Rushan deposit (37° 06'N, 121° 38'E) is hosted by intrusive assemblages, comprising the following granitoid intrusions:
i). The Kunyushan monzogranite which outcrops over an area of around 1000 sq. km and is the most important host to gold mineralisation in the area and has been dated at 157 ±4 Ma and 160 ±3 Ma. It intrudes Archaean Jiaodong Group metamorphics and contains abundant xenoliths of Archean amphibolite. It consists of quartz (36%), plagioclase (34%), K-feldspar (18%), biotite (1%) with traces of hornblende, and accessories including zircon, apatite, magnetite and titanite;
ii). The Sanfoshan porphyritic granite (K-Ar age of 99 Ma), intrudes the Kunyushan monzogranite;
iii). A dyke swarm which range in compositions from diorite to lamprophyre and intruded the Kunyushan monzogranite.
The Rushan deposit is structurally controlled by the Jiangjunshi fault, which is more than 50 km long, NNE striking and 1 to 15 m wide, which cuts the Kunyushan monzogranite and dips at 75 to 90° SE to NW.
The deposit comprises 13 auriferous quartz vein lodes, with reserves of 30 to 40 t Au. The largest is Lode 2 which contains 25 t Au and is 450 m long, ranging in thickness from 0.3 to 7 m with an average of 2.7 m. It is continuous over a down dip interval of more than1000 m between RL 120 and 900 m. Grades vary from 3 to 40 g/t, averaging approximately 20 g/t, although locally bonanza grades of 240 to 318 g/t Au are encountered. The four richest shoots with >30 g/t Au are separated by a 200 to 250 m lower grade intervals down dip. Lodes 3 and 4 contain the second and third largest reserves of 2.1 and 1.1 t Au, respectively, occurring in the hanging wall (lode 3) and footwall (lode 4) of the larger lode 2.
The ore comprises 12 to 15% sulphide minerals, with pyrite being the most abundant, accompanied by lesser amounts of chalcopyrite, sphalerite, galena, pyrrhotite, and bornite. It occurs as densely disseminated aggregates and irregular veins intergrown with quartz. Siderite locally accompanies quartz, galena and sphalerite within the ore, while tellurides are also present, including tellurobismuth, altite, calcaverite and botesite. Native gold, electrum and kustelite occur as inclusions within pyrite and other sulphides, as interstitial infillings in pyrite or as individual grains along cleavage planes of sericite and muscovite.
Multi-stage hydrothermal alteration has been observed, largely restricted to fault zones, including sericitisation, silicification, K-feldspathisation and sulphidation. Sericitisation is characterised by the complete replacement of plagioclase and partial alteration of K-feldspar with fine-grained sericite and locally coarse-grained muscovite. Sericitisation is accompanied by pyrite and fine-grained quartz, which locally form thin veinlets and fill vugs, and is followed by the precipitation of abundant sulphide minerals. The hydrothermal alteration is zoned, with a core of quartz, grading outward into quartz-pyrite, sulphides, sericite-quartz-pyrite, and an outer zone of K-feldspar. The sericite-quartz-pyrite and massive sulphide zones are the most important hosts for gold.
The Pengjiakuang gold deposit (37° 05'N, 121°16'E) is located about 25 km northwest of the city of Rushan and occupies an area of 5.73 sq. km.
The principal units in the Pengjiakuang area, include:
i). Paleoproterozoic Jinshan Group metamorphics comprising quartz-feldspar schist, mica schist, plagioclase gneiss and marble,
ii). continental sediments of the Early Cretaceous Laiyang Formation which is dominated by conglomerate with minor amounts of sandstone, totalling more than 1500 m in thickness,
iii). gneissic granite pluton of the Queshan granite which outcrops few hundred metres to the NE of the Pengjiakuang deposit.
iv). a number of mafic to intermediate dykes which intrude the sedimentary, metamorphic and granitic rocks.
The Pengjiakuang deposit is estimated to contain >30 t Au at an average grade of 4.5 g/t Au. The ore is structurally controlled by the NW trending Yazi fault, which is more than 5000 m long, 20 to 50 m wide, dips at 10 to 35° S and follows the contact between the Paleoproterozoic quartz-feldspar schist and the plagioclase gneisses or mica schists. The deposit is made up of three lodes, hosted by a cataclastic zone along the Yazi fault, to form a discontinuous WNW striking belt.
The dominant mineral assemblage in all three lodes is sericite, quartz, pyrite and calcite, with lesser K-feldspar, chlorite, chalcopyrite, galena and sphalerite. Sulphides average 4 to 6% by volume, although Lode 2 is characterised by more abundant sulphides. Au is predominantly within pyrite which typically occurs as sub- to euhedral cubes and irregular disseminated aggregates and grains ranging from 0.5 to 4 mm in size that commonly show intense deformation, with micro-fractures filled by galena, sphalerite, gold and sericite-quartz veinlets. Gold is mostly present as electrum and minor native gold, occurring as small inclusions in pyrite and, less commonly, in quartz as irregular infillings or grains in micro-fractures of sulphides, and as individual grains along cleavage planes in sericite.
Hydrothermal alteration, which is contiguous with the mineralisation, has affected almost the entire cataclastic zone of the Yazi fault. Sericitisation is the most pervasive alteration throughout the alteration zone, and is associated with disseminated sulphides and veins. Fine sericite is found as well defined selvages surrounding pyrite and quartz veins and as veins filling micro-fractures in K-feldspar. Calcite commonly crosscuts fine-grained sericite-quartz assemblages, while a late stage of sericitisation is principally composed of coarse-grained muscovite veins, associated mainly with mosaic-textured quartz. K-feldspar and chlorite are found at depth below the160 m RL within the outer parts of the cataclasitic zone.
The Guocheng gold deposit is located about 27 km northwest of the city of Rushan and is within 10 km to the NW of the Pengjiakuang mine.
The ore at Guocheng is structurally controlled by a series of deep, NE trending sinistral, strike-slip, extensional faults, of the Guocheng fault zone, with intensive tectonic-hydrothermal events during gold ore formation leaded to form multi-superposed structures. It has been proposed that the orebodies were located in ENE, NNE and NW oriented fractures secondary to the Guocheng fault zone.
The host rocks in the deposit area are mainly metamorphics of the Paleoproterozoic Jinshan Group and the Laiyang Formation of Mesozoic to Quaternary age. Magmatic rocks are predominantly fine, Neoproterozoic adamellite which spread along the NE trending fault zone to invadethe Jinshan Group.
The ore bodies of the Guocheng gold deposit are fracture-controlled, sulphide-rich veins and disseminations, formed contemporaneously with abundant dolerite, lamprophyre and monzonite dykes at ~120 Ma. The dolerite dykes contain mantle-like major element compositions with an alkaline affinity, associated with prominent subduction-type trace element enrichments, and show petrographic and chemical evidence of magma mixing that triggered exsolution of magmatic sulphide and anhydrite crystallization, preserved as primary inclusions in phenocrysts. Metal abundance ratios and isotope ratios of dolerite and bulk ore demonstrates that gold mineralisation and dolerite dykes share a common source.
The most recent source geological information used to prepare this summary was dated: 2012.
Record last updated: 20/10/2012
This description is a summary from published sources, the chief of which are listed below.
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References to this deposit in the PGC Literature Collection:
Fang Fang Hu, Hong Rui Fan, Ming Guo Zhai and Cheng Wei Jin 2006 - Fluid evolution in the Rushan lode gold deposit of Jiaodong Peninsula, eastern China: in J. of Geochemical Exploration v89 pp 161-164|
Jian-Wei L, Vasconcelos P, Mei-Fu Z, Xin-Fu Z and Chang-Qian M, 2006 - Geochronology of the Pengjiakuang and Rushan Gold Deposits, Eastern Jiaodong Gold Province, Northeastern China: Implications for Regional Mineralization and Geodynamic Setting: in Econ. Geol. v101 pp 1023-1038|
Zhou T, Goldfarb R J and Phillips G N 2002 - Tectonics and distribution of gold deposits in China - an overview: in Mineralium Deposita v37 pp 249-282|
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