Study On The Basin-Mountain Construction And The Lead-Zinc Metallogenic Regularity Of The Upper Yangtzi Block

This paper is based on the firsthand data collected from field, referring other research, guided by the basins sedimentary-tectonic evolution and mineralization, basin-mountain coupling and mineralization, regional metallogeny and other modern mineralization theory, studies the deposition-structure revolution history of the Upper Yangtze Block, investigates the metallogenic types, characteristics, and forming mechanism of lead-zinc ore deposits in this region, summarizes the time and space distribution characteristics and regional metallogenic regularity of lead-zinc ore deposits and oil and gas deposits in the Sichuan Basin of the Upper Yangtze Block and the fold areas around it, and evaluates the ore prospection. This paper makes the following research results and major understandings:Determining the tectonic evolution history of the Upper Yangtze Block and its relationship with the causes of lead-zinc deposits in the periphery of the Sichuan Basin. The Upper Yangtze Block’s stratum combination has a "double base pairs Cover" nature:the crystalline basement composed of Late Archean～Early Proterozoic metamorphic complex series and the Middle～Late Proterozoic metamorphic sedimentary-volcanic series fold basement; the lower sedimentary cover was consist of Sinian～Middle Triassic marine sedimentary carbonate rocks and the upper sedimentary cover composed of Late Triassic～Cenozoic continental clastic sedimentary rocks. The features of basin-mountain structural that was center for the Sichuan Basin and the peripheral edge of fold mountains. Since the beginning of the Late Triassic that the Upper Yangtze Block was being squeezed from three directions on stress, and the Jurassic sedimentary basin transformed into the "tectonic basin" surrounded by mountains that by way of intracontinental orogenic folding. The Lead-zinc deposits were mainly distributed in the peripheral orogenic belt of the basin in the carbonate formation, and oil-gas mineral produced in the basin interior continental strata.Proposing Basin-Mountain coupling is a necessary and sufficient condition on the Yangtze block lead-zinc deposits and oil-gas deposits formed. Basin-Mountain structural characteristics of the Yangtze Basin reflect the nature of mountain-basin coupling. Yanshanian orogeny made the thousand meters thick sedimentary cover of Yangtze block that produced drape and extrusion deformation, thereby formed the Basin-Mountain coupling. Basin mountain coupling provides dynamic conditions for activating the generation and migration of fluid into the mineral. Enrichment into minerals betides Yanshan mid-late orogenic belt-arc extension period, and Pb-Zn deposit occurs in the tensile structure of the basin edge mountains carbonate rock.Determining that Lead-zinc deposits on the Yangtze block are obvious controlled by the tertiary structure, which shows the characteristics of epigenetic mineralization. The formation of these ore-controlling structures is mainly concerned with the Yanshanian orogeny. The first-order tectonic is the orogen on the periphery of the Yangtze Block, then second-class structural is the orogen on the Yangtze block periphery of deep faults and large fold structure system, and the tertiary structure is these structures that are distributed in the carbonate strata in mining area, which include secondary faults-fold structure system, plane of unconformity, various breccia zone, paleokarst structure, interlaminar fracture system, and breccia belt between the layers.Unconformity surface controls the karst breccia, which is a kind of important ore-controlling structures.Sinian-Lower Triassic of the carbonate formationcompose the lower part of sedimentary cover, which is the main seam position of the Pb-Zn deposit of Yangtze massif, there are several unconformity surface in the sedimentary cover, it is show that the carbonate formation had repeatedly uplift to land that have generated surface dissolution, so that creating the important karst breccia type ore-controlling structure.Pb-Zn mineralization selectively occurrence in the bottom of the sedimentary cover that has all kinds of carbonate rocks, especially in the dolomite. The clastic rock of the upper sedimentary cover almost did not have Pb-Zn mineralization, which has obvious rock control characteristics, the ore rock of layer have occurred from Eozoic to Triassic, which has nothing to do with the sedimentary age of ore formation. The Pb-Zn deposits is a different types of ore deposits’combination, which is controlled by basin mountain basin peripheral orogenic belt that formed by the coupling effect of control, the seam position of deposit not only have multizone bu also have distribution characteristics of relative concentration.The difference between the slot type fold and every file type fold has different prospecting significance.The upper sedimentary cover clastic rock formation is emergence in the every file type fold of the Yangtze, there are a little of the carbonate formation in the lower sedimentary cover, which is helpless for mineral prospecting, large scale of the carbonate formation of the slot type fold outcrop at the lower sedimentary, which is a beneficial prospecting area. The Xiushan metallogenic province of the east-south of Chongqing, Dongchuan-Zoumaping of the west of Hubei, Longshan-Fenghuang metallogenic province of the west of Hunan and the south of Guizhou-the north of Guangxi are in the slot type fold deformable zone, there are large scale carbonate formation exposure at Sinian and Palaeozoic Era, that is a beneficial prospecting area of Pb-Zn deposits.Mineralization of lead-zinc deposits on the periphery of upper Yangtze block subjects to dual control of structure and stratigraphic lithology that are the main ore indicators. The Structural Sign:lead-zinc depositsare generally controlled by a variety of types and various levels of ore-controlling structure,among which faults,fold and various causes of breccia body are the factors.Faults are indispensable to mineralization so the ore exists with the fault simultaneously. Lithology sign:lead-zinc deposits, without exception, are output in carbonate rocks, especially produced in the thick-ultra thick layer of brecciated dolomite and brecciated-fine-grained dolomite. In addition, geochemical markers, geophysical markers, mineralized outcrops markers, wall rock alteration and geomorphic sign are also important prospecting mark.In the lead-zinc mineralization units in upper Yangtze region are divided into four levels on the basis of the study of the genesis, geological conditions and metallogenic regularity:I grade mineralization units are the system of basin-range coupling on the edge of Yangtze block, controlling the genetic types and distribution of MVT-type lead-zinc deposits on the entire periphery of the Sichuan Basin; Ⅱ grade mineralization units are the metallogenic belt the dominated by deep faults and a large composite fold; Ⅲ grade mineralization units are metallogenic area dominated by the regional faults, broken hole and fold control; IV grade mineralization units are the Pb-Zn Ore Field controlled by the secondary faults and anticlinal fold system,produced within all types of carbonate rocks in the lower portion of the sedimentary cover.In accordance with the favorable degree of mineralization, prospecting potential and related external conditions, the prospective areas delineated are identified as A, B, C.A:metallogenic geological conditions are very favorable,there are high strength of geophysical and geochemical anomalies, prospecting signs developed considerably and known deposits (ore occurrences) exsited; Class B:metallogenic geological conditions are favorable, there are certain geochemical anomalies,prospecting signs developed and known deposits (ore occurrences) exsited; C grade: metallogenic geological conditions are comparatively favorable, there are geochemical anomalies or prospecting signs developed. This article identifies 11 prospecting targets,and offers the basis of delineation, prospective evaluation and recommendations for future work.There are mainly three aspects of the innovation point in the topic:(1) Determine that the sedimentary and tectonic evolution of the Yangtze block controls the deposits and the formation of oil and gas mineral and its space-time distribution rule. The sedimentary and tectonic evolution history of the Yangtze block formed characteristics with "double cover and doublebase" in the strata combination of the upper Yangtze block. Since the late Triassic, the Yangtze block has been squeezed from three directions on stress, and the Jurassic sedimentary basin influenced by intense of intra-continent orogenyfolding in Yanshanian was transformed into "tectonic basin" surrounded by the mountains, its structure characteristics is that the center is Sichuan basin and the peripheral is fold mountain system. Pb-Zn deposit is distributed in the varioustypes of carbonate rocks in the sedimentary cover of the lower part of basin’s peripheral orogeny belt, while the oil and gas was produced inside upper sedimentary cover of continental strata in the basin.(2) Propose that the Pb-Zn deposits in the Yangtze block peripheral is the product of mountain-basin coupling.Mountain-basin coupling effect isa necessary and sufficient condition for Pb-Zn deposits formation.Theenergy and momentum of activation, migration and enrichment of ore-forming elements in the mineralization mainly comes from mountain-basin coupling effect.The formation and spatial distribution of Pb-Zn deposits are controlled by mountain-basin coupling effect, the metallogenic epoch is the back-arc extension period of orogeny belts in middle and lateYanshanian, the genesis of mineral deposit is basin hot brine type filling-metasomatismtype (MVT).(3) Determine that the Pb-Zn deposits in Yangtze block are obviously controlled by tertiary structure, the breccia formed by the ancient karst is a kind of important ore-bearing and ore controlling structure in mining. The primary structure is Yangtze block peripheral orogenic belt, the secondary structure is large-scale structure system with orogenic belt fracture and folding, the tertiary structure is secondary fracture-fold structure system within the area of carbonate strata distribution, which shows the characteristics of epigenetic mineralization. Significantly, there exits multiple unconformitiesespecially in the lower part of multiple sedimentary cover profile in the upper Yangtze block, showingthe carbonate rock formations have risen uplift to land surface more than once, with dissolution and formation of the ancient karst, the karst breccia, making up the important ore-bearing space.