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黄钾铁矾是干旱-半干旱地区硫化物矿床风化壳中常见的表生矿物.对表生黄钾铁矾进行精确的40Ar/39Ar定年和H-O同位素组成分析,不仅可以直接限定大陆化学风化和硫化物矿床次生富集的时间和历史,而且可为区域古气候演变和构造隆升等重大地质事件提供关键信息.本文对青藏高原东北缘祁连山地区白银矿田折腰山块状硫化物矿床风化壳中表生黄钾铁矾进行了40Ar/39Ar年代学和H-O同位素地球化学的初步研究,为祁连山地区新生代古气候条件的分析提供新的资料和思路方法.折腰山矿床的表生黄钾铁矾主要有两种产状:一种是赋存于风化壳顶部坡积物中的块状黄钾铁矾,另一种是风化壳中切割容矿岩石的脉状黄钾铁矾.块状黄钾铁矾具有板状晶形,K2O含量为8.21wt%~8.31wt%,两个样品的40Ar/39Ar年龄分别为41.2±0.4和37.1±0.3 Ma,对应的δD值分别为-156‰和-133‰,δ18OSO4值为2.5‰和2.6‰.脉状黄钾铁矾具有六方双锥状晶形,K2O含量为2.44wt%~2.72wt%,两个样品的40Ar/39Ar年龄分别为3.3±0.1和3.2±0.1 Ma,对应的δD值为-160‰和-158‰,δ18OSO4值是2.5‰和2.8‰.黄钾铁矾的40Ar/39Ar年龄和H-O同位素组成特征表明,白银矿田折腰山矿床至少在始新世中期就已隆升到地表并接受了长期的化学风化和矿床的次生富集,其中晚始新世和晚上新世的2次风化事件记录了白银地区干旱-半干旱气候条件下2次相对湿润的气候,且晚上新世比晚始新世的温度低.对祁连山地区硫化物矿床风化壳年代学和稳定同位素地球化学的进一步系统研究有可能为祁连山和青藏高原东北缘新生代以来的构造隆升、气候变化和矿床次生富集等重要地质事件提供制约.
Jarosite is a common epigenetic mineral in weathering crust in arid and semi-arid regions.Analysis of precise 40Ar / 39Ar dating and HO isotopic composition of epiphytic jarosite not only directly limits continental chemical weathering and Sulfide deposits secondary enrichment time and history, but also for the regional paleoclimate evolution and tectonic uplifting and other major geological events provide key information.This paper on the northeastern margin of the Qinghai-Tibet Plateau in the Qilian Mountain Baiyin Mountain Massive massive sulfide deposits weathering The crustal jacarandrite was used to study the 40Ar / 39Ar geochronology and HO isotope geochemistry, providing new information and ideas for the analysis of the Cenozoic paleoclimatic conditions in the Qilian Mountains. There are mainly two occurrences of hematite: one is the massive jarosite deposited in the slope of the weathered crust, and the other is the vein-jarosite cutting the ore-bearing rocks in the weathering crust. The jarosite has a plate-like crystal shape with a K2O content of 8.21 wt% to 8.31 wt%. The 40Ar / 39Ar ages of the two samples are 41.2 ± 0.4 and 37.1 ± 0.3 Ma respectively, with corresponding δD values of -156 ‰ and -133 ‰, δ18OSO4 values of 2.5 ‰ and 2 .6 ‰ .The veined jarosite has a hexagonal double cone shape with a K2O content of 2.44 wt% ~ 2.72 wt%. The 40Ar / 39Ar ages of the two samples are 3.3 ± 0.1 and 3.2 ± 0.1 Ma, respectively, corresponding to δD The values of -160 ‰ and -158 ‰, δ18OSO4 values of 2.5 ‰ and 2.8 ‰ .The 40Ar / 39Ar ages and HO isotopic compositions of jarosite indicate that the Yaojianshan deposit in the Baiyin orefield was already at least the mid-Eocene Rose to the surface and received long-term chemical weathering and secondary enrichment of ore deposits. The secondary weathering events of the Late Eocene and the Late Pliocene recorded two relatively humid climates in arid and semi-arid climatic conditions in the silver region, And the temperature of the Late Pleistocene is lower than that of the late Eocene.Further systematic studies of the weathering crust chronology and stable isotope geochemistry of the sulfide deposits in the Qilian Mountains are likely to be the structural uplift since the Cenozoic in the Qilian Mountains and the northeast margin of the Qinghai- Changes and secondary enrichment of deposits and other important geological events provide constraints.