摘要:
矿床包裹体中气液相组份,是矿床成因的重要的直接物质证据,它直接参与了成矿作用,与矿床的沉淀机制密切有关。本文研究了湖南花垣地区,产于下寒武统清虚洞组藻灰岩和鲕粒灰岩中的密西西比河谷型(MVT)铅锌矿床中,18个矿物包裹体的气相组份、气态烃组份以及气相组份的碳同位素特征。这些包裹体由水和大量的CO2(平均5.0mol%),气态烃(平均1.1mol%)和少量的CO、H2组成,气态烃中CH2的含量为89.54%,而δ13CCH4=-27.08‰,δ13CCO2=-17.28‰(PDB)。包体气相组份的这些特征表明:包体气相组份中,确有烃类存在,包体中气态烃和CO2是有机成因的;气态烃可能有多个来源层,而矿床的沉淀机制可能与流体在矿床就位位置上和早已存在的古油气藏的混合作用有关。
Abstract:
The fluid inclusion aqueous solutions and gas composition is important material evidence for genesis of ore deposits,which is direct participant of mineralization and closely related to depostional mechanisms.The paper has studied the characters of fluid inclusion gas composition,gaseous hydrocarbon composition and carbon isotope of gas from 18 samples in Huayuan Mississippi Valley-type Lead-Zinc deposits which occured in algal limestone oolitic-limestone and muddy limestone of Lower Cambrian Qingxudong Formation.The characters are that: 1.There are a little organic inclusion in ores which has been comfirmed with fluorescence microscope that a few circular organic inclusion or organic remains give out bright yellow or green-blue fluorescence. 2.Most analyzed inclusions consist of H2O with CO2 (average 5.0mol%),gaseus hydrocarbon (average 1.1mol% ) and smaller amounts of CO and,H2,etc.The content of H2O is stable and the content of CO2and hydrocarbon is various in inclusion.Gas composition of inclusion is the same between sulfides and gangue minerals,but in sulfide with different characters. 3.Methane (CH4) is the main part in hydrocarbon composition of the most inclusionsbut the content is notgreater than 95% (average 84.89%),in inclusion of sphalirite at different host rocks,which is difference,the methane content in inclusion of spharilith at light gray limestone (averge 92.65%) is more than the spharilite at gray muddy limestone (average 84.89%). 4. δ13C of methane in inclusion of main mineralization stage ranges from -27.97‰ to -26.13‰,average -27.08‰ (PDB),δ13C of CO2 in inclusion of main mineralization stage can be distinctly divided into two parts,the chief one in the main mineralization stage ranges from -19.43‰ to -14.5‰,average -17.28‰(PDS),the second one at the same time and that in the late mineralization stage are rather large (-8.12‰～3.0‰,average -3.71‰), suggesing that the main origin of CO2 in inclusion is related to the thermal degradation of organic matter. Above-mentioned characters of inclusion gas composition suggest that the organic matter really occurred in the gas composition of inclusion,the gaseous hydrocarbon and CO2 is organic origin in fluid inclusion;the hydrocarbon possibly has some source bed,and the depositional mechanism is possibly related to mixture of aqueous solutions with a pre-existing old oil-gas accumulation at the sites of deposition.
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