VULNERABILITY OF PROXIMITY INDICATORS BY TECTONO-METAMORPHISM IN THE SEDIMENT-HOSTED BASE METAL DEPOSITS TSONGOARI, NAMIBIA AND DALNESAPADNY, KAZAKHSTAN

Proximity indicators of hydrothermal deposits, exceeding the limits of ore bodies, are based on the geochemical dispersion of pathfinder elements and/or the hydrothermal alteration of the host rock by ore-forming fluids. The special development of proxis is dependent on the surrounding lithologies and on genetic factors, which control the formation of the deposits. The aim of this study is the evaluation of the vulnerability of such "vectors to ore" by different metamorphic overprint in the same type of deposit. This is verified by a supraregional study on the sediment-hosted Pb-Zn(-Cu-barite) deposits Tsongoari (upper greenschist facies) and Dalnesapadny, Zhayrem (sub-greenschist facies). Vertical zonation patterns of hydrothermal/clastic component ratios (Spry et al., 2000) such as Fe^T+Mn/Al, Fe^T/Ti, Ba/Ti and Sr/Ti in iron formations of the Tsongoari and Dalnesapadny deposits appear to be consistent indicators towards ore; metal content and -ratios such as Pb, Cu, Pb/Zn and Pb/(Pb+Zn+Cu) also increase with proximity to the orebody. Elevated values of a modified alteration index AI-M3 after Large et al. (2000) occur with proximity to the main ore zones. At Tsongoari metamorphism and deformation destroy and reset pre-tectonic fluid inclusion populations. Thus, only in a low temperature regime FI's seem to be reliable indicators of ore fluid temperatures. Mg/Mg+Fe-ratio and Zn- and Cu-content of biotite in and around the iron formation of the Tsongoari deposit increase towards the exhalative formation. Chondrite-normalised REE pattern of the Tsongoari exhalative units are highly fractionated and have a negative Eu anomaly, reflecting an elevated detrital component in the depositional environment. Hydrothermally formed apatite, fluorite, biotite and Ba-enriched feldspar are associated with coticules. Alternative proxis such as thermometric data based on trace elements in ore minerals and stable isotope ratios of mineral pairs, as well as alteration halos are being evaluated for both ore-forming systems.