摘要
Recently, a, new type of skarn Sn ore formed bY B-F-metasomatism has been found in the central part of the Malage ore field at Gejiu, Yunnan Province, which contains 1--7% Sn. The principal Sn minerals are nordenkioeldine hydromagno-cassitcrite, hydro eassiterite, etc., accounting for about 4%. Cassiterite is rarely seen (less than 0.2%).Outward from the interior of skarns are distinguished four alteration zones. Ore solutions were rich in AL and Si in the early stage of skarnization, and became enriched in Fe, Mg, Sn, B, F, H2O, etc. in the late stage. Two episodes of hydrothermal metasomatism of B and F took place during post-skarnization, and the different alteration zones may be due to reaction between B-and F-bearing hydrothermal solutions and country reeks (calcareous carbonates). The stability of the metasomatic minerals in controlled by the volatile components μB2O3, μCO2, μF2O-1 and μF(OH)-1. It has been concluded from the discussion in terms of the system CaO-SnO2-SiO2-H2O-B2O3-CO2 Fo-1 F2 o-1 proposed by Burr (1978) and the topological diagrams on chemical composition constructed by the author that nordeuskioeldine was formed in the exhaustion of Si at about 400℃ in the skarn environment, where metallogenetic conditions are characterized by rich oxygen but poor sulfur, and high boron hut low fluorine, while hydromagno-cassiterite and hydro-cassiterite were formed at the lower temperature (about 150℃) by hydrothermal metasomatism of fluorine. In comparison with the metallogenetic conditions for adjacont inner-skarn Sn ores and other Sn ore deposits at Gejiu, the role of the characteristic elemental association Sn-B-F is emphasized in this paper.
Recently, a new type of skarn Sn ore formed by B-F-metasomatism has been found in the central part of the Malage ore field at Gejiu, Yunnan Province, which contains 1-7% Sn. The principal Sn minerals are nordenski(?)ldine hydromagno-cassiterite, hydro cassiterite, etc., accounting for about 4%. Cassiterite is rarely seen (less than 0.2%). Outward from the interior of skarns are, distinguished four alteration zones. Ore solu-tions were rich in Al and Si in the early stage of skarnization, and became enriched in Fe, Mg, Sn, B, F, H20, etc. in the late stage. Two episodes of hydrothermal meta-somatism of B and F took place during post-skarnization, and the different alteration zones may be due to reaction between B-and F-bearing hydrothermal solutions and coun-try rocks (calcareous carbonates). The stability of the metasomatic minerals in controlled by the volatile components μ,B203, μC02, μF20-1 and μF(OH)-1. It has been concluded from the discussion in terms of the system CaO-Sn02-Si02-H20-B203-C02 F0-1 F2 0-1 proposed by Burt (1978) and the topological diagrams on chemical composition cons-tructed by the author that nordenski(?)ldine was formed in the exhaustion of Si at about 400℃ in the skarn environment, where metallogenetic conditions are characterized by rich oxygen but poor sulfur, and high boron but low fluorine, while hydromagno-cassiterite and hydro-cassiterite were formed at the lower temperature (about 150℃) by hydro-thermal metasomatism of fluorine. In comparison with the metallogenetic conditions for adjacent inner-skarn Su ores and other Sn ore deposits at Gejiu, the role of the chara-cteristic elemental association Sn-B-F is emphasized in this paper.
出处
《地球化学》
CAS
1985年第1期37-44,共8页
Geochimica