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Duolanasayi, Saidu |
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Xinjiang, China |
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Au Ag
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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All papers now Open Access.
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The Duolanasayi and Saidu orogenic gold deposits are located in the southern Altay Mountains of Xinjing, China.
Altay Mountains are within a sequence of accreted terranes lying between the Siberian Craton to the north and the Tarim craton to the south. The Altay region is divided into two tectonic zones by the NWW-orientated Maerkakuli fault which controlled the deposition of the sedimentary rock sequences, emplacement of magmas, and the ore-forming systems in this region at least since the Devonian. This mainly ductile shear zone which has phyllitic, mylonitic and ultramylonitic features is >100 km in length and reaches a maximum width of 5 km. The northern part of the ductile shear zone also localised the Duolanasayi, Saidu and other gold deposits.
These gold deposits are hosted by terrigenous detrital rocks and marine carbonates of the Early to Middle Devonian Tuokesalei Group, which comprises six distinct lithologic units from bottom to top, dominated overall by marine clastic rocks. The stratigraphically from the lowest unit is composed of i). conglomerate, sandstone, and siltstone, within a fining upwards succession; ii). well-graded sandstone and siltstone with some mudstone; iii). mudstone with thin siltstone and fine sandstone; the reduced sedimentary rocks contained disseminated marine pyrite; iv). nerito-paralic facies, consisting of clean and dirty limestones; v). carbonaceous- and calcareous siltstone; and vi). sandstone and siltstone.
The third lithologic unit is the main gold host and can be further sub-divided into five distinct layers, from bottom to top of: a). dark gray carbonic-bearing phyllite, metasiltstone, and siliceous slate; b). green-gray meta-siltstone with medium- to fine-grained graywacke; c). gray and green-gray phyllite, siltstone, and graywacke; d). dark-gray, thinly-bedded pelite- and reef-bearing limestone; and e). white to white-gray medium- to thickly-bedded crystalline limestone and biodetritusbearing limestone. These strata strike at 285 to 305° and dip steeply (~65°W).
Three biotite granite plutons (Sarewuzeng, Kelibayi, and Donggele) occur in the area of the Duolanasayi deposit, surrounded by narrow (2, suggesting a calc-alkaline composition.
The Habahe biotite granite pluton is exposed to the north of the Saidu deposit, with a biotite granite core rimmed by a border facies of granite-porphyry.
Duolanasayi
The Duolanasayi gold deposit is composed of a three groups of mineralised bodies distributed along a 20 x 1 km zone of fault splays cutting Middle Devonian greywacke, phyllite, and carbonate along the margins of the hornfels that are associated with the 300 to 290 Ma biotite granite pluton. Locally, granodiorite and plagiogranite dykes, younger than the biotite granite pluton, host the orebodies. Both the gold-bearing veins and the parallel dykes are localised along the limestone/clastic rock contacts within the Devonian rocks. The gold occurs both in quartz veins and disseminated in the wallrocks.
Each each of the three groups of orebodies occurs over a strike length of up to 1000 m. Widths vary from 0.5 and 15 m, and down-dip extents of 50 to 400 m. The average gold grade in these orebodies varies from from 1.2 to 14.5 g/t averaging around 6 glt Au.
Gold is predominantly hosted by granitic dykes. The auriferous veins and disseminated mineralisation are particularly well-developed where the granitic dykes intrude carbonate rocks. Quartz stockworks, generally varying from 1 to 10 cm in width (max. 50 cm). The auriferous quartz veins parallel the main shear zone and are controlled by faults. Although extension veins also occur, they are barren or only weakly mineralised. The auriferous quartz veins contain less abundant pyrite than the adjacent altered rocks. The ore minerals within the auriferous quartz veins are pyrite, molybdenite, scheelite, galena, altaite, chalcopyrite, sphalerite and electrum (or native gold). The gangue minerals include quartz, albite, ankerite, calcite, white mica, sericite, chlorite, and rutile.
The main alteration styles include silicification, potassic (muscovite, sericitc), albite and carbonate alteration. The earliest ore-related alteration assemblage consists of chlorite, carbonate minerals, albite and epidote. Subsequent assemblages include a second carbonate event, partial obliteration of chlorite and epidote, and formation of albite- carbonate and sericite assemblages in shear zones. The latest stage is marked by a quartz-sericite-carbonate assemblage. Gold is very fine-grained and occurs as free particles, appearing within euhedral pyrite grains or as coatings on the surface of quartz grains.
The Duolanasayi group of orebodies has a reserve of 5.3 tonnes of contained gold with an average grade of 8.3 g/t Au (2002) and a total resource of around 30 t of contained Au.
Saidu
The Saidu gold deposit is localised in clastic and volcanic rocks of the Early to Middle Devonian Tuokesalei Group. Mylonitised parts of the Maerkakuli shear zone host the deposit, and the degree of mylonitization correlates with the gold grade. Four groups of orebodies occur in a belt that is about 18-km-long and 2-km-wide. Each group of orebodies occurs in an area that is about 4 x I km.
The Saidu orebodies are composed by auriferous quartz vein type, auriferous altered dyke type, and auriferous altered rock type. The ore-bodies parallel the mylonitic shear zone and strike at 300 to 340°, dipping 60 to 85°: SW.
The quartz vein type is dominant and mainly consists of quartz with small amounts of fine grained sulphides, hosted by phyllite along the shear zone over intervals of several hundred metres in length and around 0.25 to 10 m or more wide. The individual veins are generally several to several tens of centimeters in width. In their upper parts the vein systems consist of discontinuous and/or brecciated quartz veins, which grade into auriferous stockworks and quartz veinlets with depth. The major sulphide in the veins is pyrite (<5% in volume), with the other sulphides and oxides, including chalcopyrite, pyrrhotite, magnetite, hematite, galena, sphalerite, marcasite, molybdenite, ilmenite, and rutile. The gold-bearing minerals include native gold, electrum, petzite, hessite, altaite and rucklidgeite. Gangue minerals in the veins include massive quartz with smaller amounts of plagioclase, sericite, chlorite, biotite and carbonate minerals. Altered and mylonitized metasedimentary rocks with disseminated sulphides and gold often occur adjacent to the quartz veins.
The gold-bearing altered dykes mainly consist of dioritic and granitic protoliths which have been altered and contain hydrothermal pyrite, pyrrhotite, chalcopyrite, galena, sphalerite, molybdenite, ilmenite and rutile. The gangue mineral assemblage consists of massive quartz, with minor amounts of plagioclase, chlorite, sericite, biotite, albite and carbonates. The degree of alteration correlates with the degree of deformation of the dyke. Silicification + sulphidation + alkaline alteration are dominant in and near the ore zones, whereas chlorite and carbonate minerals are more important distal to the ores. The largest single orebody of this type varies from 70 to 200 m in length and 1.2 to 4.5 m in thickness, with a gold grade of 0.3 to 3.9 g/t.
The Saidu group of orebodies is estimated to contain in excess of 10 tonnes of gold at grades of around 4 g/t, locally up to 65 g/t Au.
The most recent source geological information used to prepare this decription was dated: 2003.
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
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Liu, Y., Zhu, Y. and Wang, D., 2003 - Shear-zone related gold deposits of the Southern Altay Mountains, Northwestern China: in Mao, Goldfarb, Seltmann, Wang, Xiao and Hart (Eds.), 2003 Tectonic Evolution and Metallogenesis of the Chinese Altay and Tianshan, Proceedings Volume of the International Symposium of the IGCI – 473 Project in Urumqi and Guidebook of the Field Excursion in Xinjiang, China: August 9-21, 2003. IAGOD Guidebook Series 10: CERCAMS/NHM London, pp 201-207
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