福建省层控铅锌矿床地质地球化学特征

作者按照涂光炽教授的分类将福建省层控铅锌矿床划分为4种类型。本文对它们的地质特征、微量元素和硫、铅同位素组成的特征作了较详细的阐述,对矿床的矿质来源作了初步的探讨。

THE GEOLOGICAL AND GEOCHEMICAL FEATURES OF STRATABOUND LEAD-ZINC DEPOSITS IN FUJIAN PROVINCE

According to the Tu Guangchi classification, the authors grouped stratabound lead-zinc deposits in Fujian province into four genetic types, namely: sedimentary -metamorphic, sedimentary-transformed, sedimentary-late hydatopneumatic su- perimposed, and epigenetic ore deposits. The ore-control stratigraphic horizons of sedimentary-metamorphic deposits are calcic rocks in Daling Formation and Mayuan Formation of Precambrian blende-galena-pyrrhotite. Sedimentary-transformed and epigenetic deposits have pyrite chalcopyrite and magnetite beside the association. There occasionally are, in addition to those minerals, dalarnite and cassiterite in sedimentary-late hydatopneumatic superityposed deposits. Composition of trace elements in all the four types of deposits is characterised by enriching of Ag, Bi and Cd. Ore minerals for four types of deposits differ in composition of trace elements. Ag, Bi and Se contents, Bi/Ag and Se/S×10-4 ratios in blende increase with sedimetary-metamorphic→sedimentary-transformed→epigenetic→sedimentary-late hydatopneumatic superimposed type. Change of Ag, Bi and Se contents in sedimentary -metamorphic deposits is smallest among the four types. Chang of Ag, Bi and Se contents in the three other types is greater than the sedimentary-metamorphic type by a factor of 2. Results of R cluster analysis show that grouping of elements for sedimentary -metamorphic and sedimentary-transformed ores generally accords well with grouping of elements for ore-bearing strata, but grouping of elements for sedimen- tary-late hydatopneumatic superimposed ore only partially accords with grouping of elements for ore-bearing strata. The origin of sulphur in the four types of deposits are different from each other. Because of homogenisation sulphur isotopic composition in sedimentary- metamorphic deposits is stable and equal, and δ34S values are always small positive numbers. The δ34S values in epigenetic deposits change widely between larger positive number and smaller negative number. The sulphur in the two above mentioned types of deposits is of normal sedimentary origin. δ34S values in sedimentary-transformed and sedimentary-late hydatopneumatic superimposed deposits are zero, a little larger or smaller than zero. The sulphur might originated from the deep crust. Lead isotoopi composition in sedimentary-metamorphic and sedimentary trans- formed deposits are stable and equal. The lead belongs to the normal common lead. Lead isotopic model age of the two types of deposits accord well with the age of ore-perserving strata. The lead is of crustal origin, Lead isotopic composi- tion in sedimetary-late hydatopneumatic superimposed deposits is characterized by mixed lead, partly originating from the ore-preserving strata, partly from the strata under the deposits. Lead isotopic composition in epigenetic deposits is characterized by U-and Th-rich abnormal lead. The lead belongs to the lead ori- ginated from the residual crust.