Caledonian formation of gold-bearing sulfide depositions in Early Proterozoic gabbroids in the northern Ladoga region     

Sh. K. Baltybaev  G. V. Ovchinnikova  V. A. Glebovitskii  I. A. Alekseev  I. M. Vasil’eva  N. G. Risvanova 《Doklady Earth Sciences》2017,476(1):992-996

We have studied Pb isotopic systems of K-feldspar, pyrite, and pyrrhotine from gabbroids and ore of the Velimyaki Early Proterozoic massif in the northern Ladoga region in the southeastern part of the Fennoscandian Shield. The isochronous Pb–Pb age of sulfides has been determined as ～450 Ma, which corresponds to intersection of the regression line with the lead accumulation curve with μ = 10.4–10.8; the model Pb age of sulfides is close to isochronous under the condition that the composition of lead evolved from a geochemical reservoir with an age of 1.9 Ga. The isotopic parameters of the lead in sulfides and K-feldspar indicate their formation in upper crust conditions (μ = ²³⁸U/²⁰⁴Pb > 10). From the obtained data, it follows that the isotopic composition of lead in K-feldspar corresponds to a Proterozoic age (1890 Ma) of magmatic crystallization of the rocks in the massif, and strongly radiogenic lead sulfides testify, with the greatest probability, to the later (Caledonian) formation of sulfide ores.  相似文献   

1980—2017年四川省气候变化综合区划北大核心          下载免费PDF全文

刘伟  车康利  罗斯元  刘莎  贾植杰  李逢港 《气象科学》2022,42(1):108-115

基于四川省1980—2017年主要气象要素观测资料,运用ArcGIS空间分析法,分别探讨了气温、降水量和极端气候指数的年际空间变化特征;同时建立极端气候指标体系,结合熵权法、模糊综合评价法开展综合极端气候指数区划,最终完成1980—2017年四川省气候变化综合区划。研究表明:1980—2017年四川省极端气候事件的发生率呈上升趋势,从区域分布上大致表现为东高西低;根据四川省气温和降水量变化速率区划、综合极端气候指数区划,将四川省划分为6个气候变化区,其中,川东北地区综合气候变化速率最快。  相似文献   

uvbyß photometry of the components of Trapezium-type multiple systems     

G. N. Salukvadze  G. Sh. Javakhishvili 《Astronomische Nachrichten》1995,316(5):275-280

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