Metallogenesis Of Endogenic Gold Deposits In Heilongjiang Province

Heilongjiang province is located in the eastern part of Hinggan-Mongoliaorogenic belt. But there are only34gold deposits in it, which do not match well with goodmetallogenic conditions of the region. Based on regional geology and geophysical data,combining material from zircon geochronology, petrology and geochemistry, it was thoughtthat endogenetic gold geodynamic settings of Heilongjiang province belongs to evolution,transition and superposition between Paleo-Asia tectonical domain and circum-Pacific one.Under the transition and subduction of Pacific oceanic plate, the lithosphere underwent strongcompression and thickening. Then a large scale of detachment, extending and thinninghappened, which resulted in a large scale of structural-magmatic activities and mineralization.The coupling relationship between regional geodynamic evolution and metallogenesis areconcluded as follows:(1) In the late Permian in the late hercynian (260-250Ma),Songnei-Jiamusi block collided with North China plate during closing of Paleo-Asia ocean inLate Permian. Orogenic gold deposits such as Laozuoshan and Yingchengzi etc. depositsdeveloped and crustal continuum model occurred.(2) In the early Yanshanian (190-170Ma),this region came into circum Pacific tectonic domain, strong subduction of Pacific plate andregional geotectonic settings changed basically. The continental margin of western Pacificocean transferred into active one, which controlled a series of large-scale veinlet-network-type Mo deposits such as Huojihe and Luming, skarn-type Mo polymetal deposits andDa'anhe skarn-type gold deposit. The granites that were thought to the late Triassic mostlyintruded in this era.(3) In late Yanshanian (120-100Ma), a large scale of detachment,extending and thinning of lithosphere happened after subduction of Pacific plate in the earlyCretaceous. Epithermal gold deposits like Dong'an, Sandaowanzi ones and Meso-epithermal vein type ones like Shabaosi deposit developed.The author researches typical gold deposits such as the orogenic gold deposits(Laozuoshan, Yingchengzi) under late Paleozoic collision, Skarn type gold deposits (Da'anhe)under the Mesozoic to the early-middle Jurassic compression and thickening of lithosphere,epithermal gold deposits (Sandaowanzi, Dong'an and Sipingshan) and meso-epithemalvein-type gold deposits (Shabaosi) under the early Cretaceous extensional thinning oflithosphere by the methods of field survey, fluid inclusion researches and metallogenicgeochronologies. Then the author determines major genetic type of deposits and buildsendogenetic gold metallogenic models and series in the studying area. The creativeachievements have been got as follows:(1) According to SHRIMP U-Pb dating of zircons inintrusive rocks and hydrothermal monazites related to metal minerals and Re-Os dating ofmolybdenites in ores, it was the first time to consider that there are two stages ofmetallogenesis in Laozuoshan gold deposit. And the author determined that the age ofmetallogenic gneiss granite is256±3.1Ma, and the Re-Os isochron age is256±1.3Ma in theearly metallogenic stage. So it was thought that the early metallogenic stage is256Ma in thelate Hercynian, which is related with continental-continental collision during closing ofPaleo-Asian Ocean. The author also determined that the age of pre-mineralization diorite is106±1.0Ma, the age of post-mineraliztion felsite is100.9±1.6Ma, and the hydrothermalmonazites SHRIMP U-Pb age is105.3±3.2Ma. So it was considered that the late metallogenicstage is105Ma in late Yanshanian, which is related with the detachment, extending andthinning of the lithosphere in the early Cretaceous. Hydrothermal monazites developcommonly in hydrothermal deposit, so they can be used to date directly the metallogenic ageof mineral deposits. Then the monazite dating has a better prospect and is worth to popularizewidely.(2) LS-type of epithermal gold deposits is the most extensive and largest type of golddeposit in Heilongjiang province. The age of typomorphic adularia can representmetallogenic age, while adularias develop well in Dong'an, Tuanjiegou, Jinchang golddeposits. It was the first time to date Ar-Ar age of Adularia formed during mineralization andalteration process in Dong'an gold deposit as105.14±0.7Ma, which is consistent with the109.6±1.7Ma of eight zircon206Pb/238U age from metallogenic quartz porphyry. The successof adularia dating has important reference value to date the metallogenic ages of theepithermal gold deposits like Dong'an, Tuanjiegou and Jinchang.(3) The predecessors considered that Shabaosi gold deposit that is located among sandstone belongs to alterationrock-type, epithermal-mesothermal or orogenic gold deposits. The author thought that theearly Cretaceous (133±5Ma and142.79±2.11Ma) bimodal diorite porphyrite, diorite,lamprophyre, gabbroporphyrite, rhyolite porphyry and granite porphyry were related spatiallywith gold mineralization. They are pre-mineralization intrusive rocks formed underextensional regime. Major ore-controlling structures are normal faults formed in extensionaland strata-cutting conditions rather than thrust faults or interbeded ones thought by thepredecessors. Combing with the characteristics of fluid inclusions of Shabaosi gold deposit, itwas thought that the deposit belongs to meso-epithermal vein-type deposit controlled bynormal faults, and the metallogenic age of it is consistent with the early Cretaceous(120-100Ma) large scale mineralization, whose mineralized type match well with the secondstage of mineralization in Laozuoshan gold deposit. Then the author proposed that there aretwo series of metallogenic systems which consist of the shallow LS-type epithermal goldmineralization and deep porphyry-skarn-type mineralization. And the deepporphyry-skarn-type mineralization may be the further prospecting target.(4) According tostudy on the geodynamic settings and geological characteristics of Sandaowanzi gold depositthat is one of richest deposit of the world, it was the first time to propose that the origin offluid is primary mantle-derived fluids. Sandaowanzi gold deposit belongs to LS-typeepithermal Au-Ag-Te deposit. There are lots of Au-Te-bearing sulfides in ores. Te isdeep-source element, and lots of Te-bearing sulfides are important mineral symbols ofmantle-derived metallogenesis. Au and Te migrate and enriched up to the crust because ofmantle degassing while early lithosphere extending and thinning. The alkaline rocks, whichare often derived from upper mantle, related to Sandaowanzi gold deposit also contain Te.And the S and Pb isotopic compositions from this deposit also show that the sources of S andPb are derived from the upper mantle.Based on the previous researches, the author analyzed the gold metallogenic conditionsin Heilongjiang province and summarized the spatio-temporal regularities of gold deposits init. Especially discriminating NW-striked upper mantle depression, NW-striked low valuezone of gravity anomalies (possibly resulted from deep acid-intermediate rock bodies),NW-striked linear structures (from explaination of gravity anomalies) in Xiao Hinggan Lingand Heilongjiang tracing-tension-joint fault, the author ascertained that there is a NW-striked epithermal and meso-epithermal vein-type gold metallogenic belt in Xiao Hinggan Ling.Finally, in order to prospect endogenetic gold deposit, the following key problems must beconsidered further:(1) The geodynamic settings are the basic ore-controlling factors for oredeposits forming, which are the basic and necessary conditions for ore prospecting.According to these conditions, ascertaining genetic type of gold deposit in prospective area isthe most important mission.(2) The major genetic types of gold deposits are epithermal andorogenic ones. The former one has shallow metallogenic depth, so studying on denudation(including different denudation) and conservation may help instruct prospecting. And the typeof epithermal gold deposit in Heilongjiang province mostly belong to the LS-type golddeposit, so the HS-type gold and LS-type Ag deposit may have good prospecting potentials.The latter one has deep metallogenic depth, exactly calculating the metallogenic depth ofdifferent levels of orogenic gold deposits can provide reliable data for regional oreprospecting and deep mineral prospecting.(3) Choosing effective exploration methods basedon the basic geological characteristics of gold deposit and mineralized enrichment regularitiesis the key for found and exploration of them. And occurrence regularities of ore bodies likecluster, lateral corresponding, isometry distribution, segment enrichment, and pitch can beused effectively for ore prospecting.