摘要
在分析已有资料和参与地矿部“七五”重点科技攻关项目(“三江”滇西片课题)的基础上,笔者认为,金顶超大型铅锌矿床是在长期活动的地质构造环境、良好的聚矿陆内地堑盆地、喷溢沉积作用的成矿机制、同生断裂的长期活动、有利成矿的岩相及古水文条件、推覆构造的掩埋作用等特定条件下形成的。
The Jinding superduty-scale lead-zinc ore deposit gathered within four knl^2 has specially metallogenic geology conditions. The ore deposit is situated on the. western side of the Pijiang fracture and in the northern part of the graben basin of Lanping-Yunlong Tertiary Pale-ocene. The ore area presents a dome structure consisting respectively of the autochthonous system and overlying allochthonous system(nappe) and the ore-bodies occur in middle, upper members of the Paleocene Yunlong Formation (Ey^b, Ey^c)being the autothonous system. The ore deposit was formed in a tectonic setting with long-term activity. The geotectonic evolution experienced a process from stretching-compressing -restretching to recompressing, on the whole and from Carboniferous to Tri-assic, manifested itself as the open subsidence-preliminary closing—back-are extension fracture to orogeny subduction of the Paleotethystogether with a large amount of volcanic eruption and magmatic intrusion along the Lan-cangjiang and Jinshajiang fracture zones. From Jurassic to Paleocene, the in-tracontinental depression and graben had been formed. The intracontinental compression and napping happened in late Paleocene, and the mineralization appeard in the stage of Paleocene intracontinental graben to late in Pale-ocene compression, napping. The ore deposit was the upwelling sediments of intracontinental lake flo-or which is divisible into two sets of metallogenic systems. The chemical se-dimentary system of lake floor in the upper part formed the stratiform, stra-toid orebodies and sandstone type ores in which the cemented texture and imp-regnation, massive structures and weak alteration developed. The supplement system in the lower part made up lenticular, pipe, etc. irregular orebodies and breccia type ores, showing the metasomatic fusion, crystal grained textures and brecciated, veined structures and strong alteration. The metallogenic me-dium was the mixed hot water of Na-Ca-CI-SO_4 type with moderate sali-nity. The metallogenic temperatures were 150 to 250℃, and Zn/Pb+Zn ratios, 0.83 consistent with the SEDEX ore deposit. Ore lead isotopes display the fe-atures of mantle-derived and mixed crust-mantle-derived lead. S^34S values of sulfide range from-1.71 to 30.43 per mille. The Pijiang fracture of long-term activity in the eastern margin of the basin resulted in the formation of a trenched graben basin and its submarine sub-depressions acting as the space for ore fluid upwelling concentration, and caused the sedimentation of collapse breccia and active type alluvial fan fa-cies as the ore-hosting rock system. The fracture itself played the passage-way for ore fluid upwelling. The argillite in lower member of Yunlong Formation(Ey^a)underlaid the ore-bearing horizon being a good aquifuge made the deep-seated ore fluids increase their salinity and be in a superpressure state, thus flowing over into the basin for metallization along the Pijiang fracture. The Ey^b and Ey^c belonged to the sediments of breccia facies of fissure water medium and of alluvial fan facies of pore water medium provided them with migrated and deposited space after the ore fluids drained into the ba-sin. Late in the Ey sedimentation in the case of the ore-bearing depression buried by the nappe and the ore-hosting horizon closed by the upper and to-wer screened layers, the deep-seated groundwater uplifted along the fissures with the temperature and pressure increase; in shallow environment, that ma-de the ore-hosting horizon early in diagenesis further suffer pressolution, me-tasomatism, recrystallization and the epigenetic minerals appear; late in dia-genesis, the metallogenic substances were further enriched and disposed to form the ore deposit.
出处
《云南地质》
1991年第2期230-240,共11页
Yunnan Geology
