Study On The Metallogenic Regularity And Geological-geochemistry For Black Rock Series And Related Typical Deposits In Qinling Mounitains, Shaanxi

The black rock series in Qinling Mountains are made up of carbonaceous argillite, carbonaceous siliceous argillite,silicalite,argillite,marl,stone coal and carbonaceous limestone.Phosphatic podule,pyrite and barite are always found in these rocks.Geological and geochemical study shows that the black rock series were formed by hydrothermal fluids and biological action in anoxic environment.Complex metallogenic matter had multi-source.The character of biomarkers indicate that the organic matter derived from plankton, bacterium and alga.The organic compenent in some samples has the characteristic of advanced plant.Organic-carbon in Qinling black rock series could vary from low to high,the content of carbon under tectonic metamorphic rocks is less than that of other black rocks. Black rocks in Qinling are lower dissolved hydrocarbons and hydrocarbons originated from kerogen cracking for thermal decomposition in advance.The black rock series of Qinling orogenic belt can be divided into three parts(north belt, middle belt and south belt) in consideration of the geological background,rocks and metallogenic elements combination.The Miaowan Formation as the north belt black rocks formed in fringe sea which belongs to an active continental margin,and contains high K,Fe, Al and low Si,variational Na,with Toe raging from 2.52%to 4.7%.The metallogenie matter is from terrigenous component adding biological component and hot water which is relevant with basalts and granites.Combination of metallogenic elements is Mo,Ni,Cu,Pb,Zn and U. A Ni-Mo deposit was found in it.The middle belt of black rock series has more silicalite and variational Toe and lies in the bottom of Shuigoukou Formation which was from profundal or semiprofundal stagnant fault basin around paleo-uplift-belt of Qinling micro-plate.The source belt was like north belt rocks,while hot water matter could only be correlated with basalts. The combination of metallogenic element is Au-V-P-Cu-Pb-Zn-U.Au and V deposits were found in it.The south black-rock belt was formed in horst-lift basins of continental fringe which was made up of Lujiaping and Banjiuguan Formations,There are more phosphorite, stone coal,barite and witherite while less volcanic rocks in some parts.The source is continental matter,biological component and hot water related with basalts.Combinations of minerogenic element are V-Mo-Ba-P-Au and V-Mo-Au-P-Se-C.Barite deposits,witherite deposits and V deposits were found in this belt.The Ni and Mo elements of Qinyangou Ni-Mo ore are from the black rocks in Miaowan Formation,but posterior magma.According toδD-δ¹⁸O diagram,geologic feature and oxygen-isotope of ore,the ore-forming solution was intensively reconstructive meteoric water, metamorphic hydrothermal solution and small quantity of magmatic water.Forming process of ore had come through primary enriching period,regional metamorphism period,tectonic and superimposed hydrothermal solution reconstrueturing period.The main minerals are molybdenite,pentlandite and pyrrhotite.The homogenizational temperatures of inclusions in ore-bearing quartz vein were from 211.4 to 444.9℃,corresponding to middle to high temperature.The salinity of these inclusions had large scope(7.02～19.21%).Both the temperature and salinity decreased following the time sequence.The ore-body which consists in serieite carbonaceous phyllite part,which has the feature of superimposed strata deformed by tenacity-brittle shear.The ore was controlled by strata,rock,structure and hydrothermal solution.The Zhongcun-Yinhua vanadium ore was caused by sediment -diagenesisdiagenism.The ore body was in the bottom of Shuigoukou Formation.The rich ore rocks were rich in Al and K,poor in Ca,while the contrary contents are in poor-ore rocks.Ore-bearing rocks and rare-earth content,Ba has better relations between growth and decline.Better ore-forming always has more Toc or organic substance.The content of V is 75.2%in argillite(existing as isomorphism),and is 24.8%in silicalite(existing as adsorption)Xiajiadian micro-disseminated type gold deposit is a middle-large-sized sedimentary-structural-hydrothermal-reconstruction Au metal deposit hosting in black-rock-series.In this deposit,rich-ore rocks contain more Si,Fe,C and K than others.The homogenizational temperature of fluid inclusion in mineralized quartz and calcite is from 140 to 336℃,and the mineralized pressure is in the range from 370×10⁵ to 820×10⁵Pa,the mineralized salinity varied from 3.27 wt%to 5.25 wt%.The deposit has experienced pre-enriching process in Paleozoic,ductile-brittle structure and hydrothermal superposition process in Neozoic,erosion-oxidation process in subsequent time.Huangboshuwan witherite in the south belt is a marine thermal water sedimentary deposit which had been slightly rebuilt by tectonics.The major metallogentic minerals are witherite and barite.The ore body were stringently controlled by the bottom strata of Lujiaping Formation.The indicator horizon is transition-passage between silicalite and carbonaceous siltstone.The witherite was intimate inter-growth with barite and thin layer silicalite with cellophane.The discovery of sponge-spicule and foraminfera fossil indicates that the sedimentary environment was dominant by profundal depressed fault basins in marine bottom. The vanadium deposit of Liyushan is a middle-sized sediment-reformed deposit in the lower Lujiaping Formation in south belt.Clay slate and intercalated siliealite made up of the stratum and Mo is super-enriched in these particular parts.The strata had been strongly affected by tectonics and slightly affected by hydrothermal,The other features of the deposit are similar to that of Zhongeun vanadium deposit.Mineral matter of ore come from the black rock series themselves,The elements of Au, Mo and Ni are original enrichment,while V is industrial enrichment during sedimentary-diagenetic stage.The weak reconstruction had little effect on mode of occurrence of V,while strong tectonics and hydrothermal liquid made Au,Ni-Mo conglomerated during different periods.The sources of mineral elements were correlated with tectonic background, sedimentary mieroenvironment,erosion area of land and basement rocks,thermal hydrodynamics and microorganism rather than other cosmic matter.The lower content of Toc in Au deposit of Xiajiadian and Ni-Mo deposit of Qingyangou are probably caused by strong tectonics and pyrogenation process.The liquid state and gaseity hydrocarbon from Toc played an important role in the process of ore-forming.The factors such as complex lithology,active- biological processes,much thermal hydrodynamics and complete rock types are advantaged to form ore deposit.