摘要
本文通过对浙中火山岩区中最著名的武义—东阳萤石成矿区9个矿床和地层岩石的38个样品的锶同位素地球化学研究,证实了赋矿岩层下伏基底的前寒武纪陈蔡群变质岩是该区萤石矿床的主要矿源层;^(87)Sr/^(86)Sr和F/sr比值表明,萤石成矿过程中约57—76％的氟和40—50％的锶(钙)来自陈蔡群变质岩,来源于上地幔的氟平均不超过24％。^(87)Sr/^(86)Sr比值和其它稳定同位素等资料,也揭示这些萤石矿床的形成主要与古地热水环流汲取作用有关,从而对其成因属于火山热液矿床的传统认识提出了异议。
Fluorite deposits in Wuyi-Dongyang fluorite minerogenic area occur mostly in Late Jurassic volcanic rocks and secondarily in Early Cretaceous sedimentary rocks and metamorphic rocks of precambrian Chencai Group. Orebodies are unexceptionally in the vein-like form and fluorite mineralization has an age of some 70 Ma. The ^(87)Sr/^(86)Sr ratios of fluorite-related Late Jurassic volcanic rocks, Early Cretaceous sedimentary rocks and metamorphic rocks of Precambrian Chencal Group are respectively 0.7085-0.7289 (averagely 0.7151), 0.7137-0.76d0 (averagely 0.7276) and 0.7456-0.9103 (averagety 0.7940). Fluorites from fluorite deposits in different types of wall rocks have fairly similar strontium composition, and ^(87)Sr/^(86)Sr ratios vary in the range of 0.7306-0.7710, with the average being 0.7500 or so. These data indicate that the strontium isotope composition of fluorite-forming fluids was controlled by mixed system of strontium isotopes derived from different sources, The threecomponent mixing model and F/Sr ratios of the recks suggest that, during the mineralization of fluorite, about 57-76% F and 40-50% Sr (Ca) came from basement metamorphic rocks of Precambrian Chencai Group, while F derived from upper mantle did not exceed 24% on the average. This result demonstrates convincingly that metamorphic rocks of Prccambrian Chencai Group is the main source bed for fluorite deposits in this area. δ^(18)O and δD values of water in fluorite inclusions are respectively + 1.3-1.4‰. and -48.23-68.00‰, showing hydrogen and oxygen isotopic composition characters of geothermal water. It is believed from the above Sr, H, O isotopic data and field studies that, rather than being of volcanic hydrothermal origin, the fluorite deposits in this area should mainly attribute their formation to circulation and drawing of paleogeothermal waters.
出处
《矿床地质》
CAS
CSCD
北大核心
1989年第3期65-74,共10页
Mineral Deposits
