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苗龙金锑矿床位于贵州三都-丹寨金锑汞成矿带,矿体赋存于上寒武统三都组海相碳酸盐岩中。本文对该矿床的成矿期方解石微量元素含量、Sr-Nd同位素组成进行了研究。结果表明,该矿床成矿期方解石稀土元素总量变化范围大(5.98~139μg/g,平均值为43.7μg/g),在球粒陨石标准化稀土元素配分模式图中大多数方解石样品具有轻稀土富集特征((La/Yb)_N=1.84~9.18,(Gd/Yb)_N=2.55~6.14),少量样品表现为中稀土富集特征((La/Yb)_N=0.33~1.39,(Gd/Yb)_N=1.29~2.24)。该矿床成矿期方解石样品不具有Ce异常(δCe=0.97~1.19),但具有Eu异常(δEu=0.61~1.72),指示其形成于相对还原条件下。方解石样品的~(87)Sr/~(86)Sr值为0.7108~0.7144,平均值为0.7119,高于赋矿围岩的~(87)Sr/~(86)Sr值(0.7090),表明成矿流体相对富放射成因锶,其不可能主要由赋矿的三都组灰岩提供,而可能来自富放射成因锶的前寒武纪基底。Sm-Nd同位素研究表明,该矿床成矿期方解石样品可构筑两条Sm-Nd等时线,其对应的等时线年龄分别为273±14 Ma和272±43 Ma,但与地质背景不符,因此该次方解石Sm-Nd同位素定年等时线无地质意义。这种假等时线现象可能是由成矿流体初始~(143)Nd/~(144)Nd不均一造成的。方解石ε_(Nd)(0)(-14.02~-9.48)远小于0,指示成矿流体中的Sm和Nd来源于陆壳。
The Miaoling gold antimony deposit is located in the Sandu-Danzhai Au-antimony-mercury metallogenic belt of Guizhou Province. The ore body occurs in marine carbonate rocks of the Upper Cambrian Sandu Formation. In this paper, the trace element content and Sr-Nd isotopic composition of calcite in the ore-forming stage were studied. The results show that the total amount of rare earth elements in the calcite in the ore-forming stage varies greatly (5.98-139 μg / g, with an average value of 43.7 μg / g). Most of the calcite samples in the normalized REE pattern of chondrulesite have light rare earth (La / Yb) _N = 1.84 ~ 9.18, (Gd / Yb) _N = 2.55 ~ 6.14) /Yb)_N=1.29~2.24). The mineralization calcite samples do not have Ce anomalies (δCe = 0.97-1.19) but Eu anomalies (δEu = 0.61-1.72) indicating that they are formed under relative reduction conditions. The ~ (87) Sr / ~ (86) Sr values of calcite samples ranged from 0.7108 ~ 0.7144 with an average of 0.7119, which was higher than the value of ~ (87) Sr / ~ (86) Sr The ore fluids are relatively radioactively-producing strontium, which is unlikely to be mainly provided by the ore-bearing Sandu limestone, but probably from a pre-Cambrian basement rich in radiogenic strontium. The Sm-Nd isotopic study shows that two Sm-Nd isochronal lines can be constructed in calcite samples during the mineralization, with corresponding isochron ages of 273 ± 14 Ma and 272 ± 43 Ma, respectively, but not consistent with the geological background. Therefore, the calcite Sm-Nd isotopic dating is of no geological significance. This pseudo isochronal phenomenon may be caused by the initial ~ (143) Nd / ~ (144) Nd heterogeneity in the ore-forming fluid. The calcite ε_ (Nd) (0) (-14.02 ~ -9.48) is far less than 0, indicating that Sm and Nd in the ore-forming fluids originate from the continental crust.