Abstract:

The Gangdese belt is the largest copper polymetallic metallogenic belt in China. A historical breakthrough has been made in porphyry-copper polymetallic prospecting by the discovery of a series of large-giant deposits, including the Qulong and Jiama deposits, in the eastern Gangdese belt. In contrast, very little geological research has been done in the western Gangdese belt due to the complex tectonic background and poor road conditions. The western Gangdese belt has different crustal structure and properties from its eastern counterpart, where heterogeneous mantle properties, crust-mantle interaction, and the large volcanic rock cover led to great uncertainty and controversy over its genetic type and ore prospecting potential. In this contribution, with the substantial support of the Ministry of Science and Technology and the China Geological Survey, we made great progress or breakthroughs in clarifying the regional metallogenesis and in the discovery of new rock types, mineral species and deposits, through the application of the geo-anomaly theory developed by academician Zhao Pengda, and through a series of technological innovations, target selection, and target explorations. We discovered a number of Ag-Sn-Au-Cu-Pb-Zn-W deposits with medium to large prospecting prospects, such as the Bangbule Pb-Zn-Ag-Cu, Balong Ag-Pb-Zn-Sn, Dajiacuo Ag-Pb-Zn, Nuocang Pb-Zn-Ag-W, and Sangmola Sn-Au deposits. We also found very different metallogenic processes of the eastern and western Gangdese belt. In the western Gangdese belt, in addition to the traditional porphyry Cu-Mo-Au and skarn Fe-Pb-Zn-Cu(Ag) deposits, the continental (sub-)volcanic rock-related epithermal Ag-Sn(Au) polymetallic deposits (especially Ag-Sn or independent Ag deposits) have the highest prospecting potentials. This deposit type is mainly controlled by the coupling of ancient basement, thrust-nappe structure, sub-volcanic structure, sub-volcanic rocks, and late Paleozoic terrane. The geochemical anomaly elements are mainly Ag, Pb, Zn, Sn, Cu, Au, As, Sb, Mn, and so on, among which the rich elements Ag, Sn and Au have characteristic geochemical anomalies, therefore they can be distinguished from simple skarn and magmatic-hydrothermal deposits. These deposits are closely related to the stage and genesis of volcanic magmatic activities, and mainly distributed in the Gangdese volcanic magmatic arc, and arc-back fault uplift zone. Thus, six metallogenic series were recognized as (1) the porphyry Cu-Au series related to late Triassic arc magmatism; (2) the skarn-epithermal Fe-Ag-Pb-Zn (Sn) series to early Cretaceous arc magmatism; (3) the skarn Fe-Cu-Pb-Zn(Ag) series to late Cretaceous magmatism; (4) the porphyry skarn Fe-Cu-Mo-Pb-Zn(Ag) series to Paleocene Eocene intermediate acid intrusive rocks; (5) the epithermal Ag-Pb-Zn(Sn-Au) series to Paleocene continental (sub-)volcanic rocks; and (6) the porphyry skarn epithermal Cu-Mo-Au-Pb-Zn-Ag series to Miocene magmatism. These metallogenic series define the mineral species, prospecting types, and prospecting direction of the western Gangdese, and objectively demonstrate its resource potential. According to the mineralization condition, distribution of known deposits, and prospecting potentials, five ore clusters were further delineated in the western Gangdese. They are the Longgeer Pb-Zn-Fe-Cu, Nixiong-Ria Fe-Cu, Zhunuo-Luobuzhen Cu-Mo-Au, Chagele-Nuocang Ag-Sn-Pb-Zn-Cu-Mo, and Rebuka Ag-Sn-Pb-Zn-Pb-Zn ore clusters. In particular, the ore-rich Zhunuo-Luobuzhen and Chagele-Nuocang areas show great prospecting potentials. They will become the most important Cu and Ag-Sn polymetallic exploration bases in the western Gangdese belt, hereto providing a decision-making basis and direction for further prospecting and exploration in the region.

Key words: mineralization, metallogenic series, new discoveries in ore prospecting, new minerals, new types of deposit, western Gangdese belt, Tibet