LEAD-ISOTOPE COMPOSITION OF POTASSIC FELDSPARS FROM MESOZOIC INTRUSIONS OF TRANSBAIKAL

Abstract

Knowing the lead-isotope composition of potassic feldspars in ore-bearing intrusions should show whether or not endogene ore mineralization is genetically related to them and many sometimes allow their age to be estimated as well. Therefore, we analyzed the lead-isotope composition of potassic feldspars (K-spars) from granitoid plutons of the Shilka and the South Aga structural zones in Transbaikalia. The intrusions of the Shilka zone are mostly hyabyssal and belong to the Amudzhikan-Sretensk complex. Their cores consist of porphyritic granite, and their marginal facies and satellite stocks of granite porphyry vein formations include granite and aplite dikes and pegmatite veins. The granitoid rocks studied in this zone can be geochemically classified as palingenic granitoids of the calcalkalic series. Our study of the lead-isotope composition of K-spars has revealed a distinct difference between the palingenic calcalkalic granitoids and plumasitic leucogranites, and has confirmed the relationship of the endogene ore mineralization to each of these geochemical igneous rock types, established earlier from the isotope distribution in ore lead.