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摘要
Beiya gold-polymetallic ore district found in northeastern Yunnan province in the last few years, located in the middle-southern section of the eastern Xizang-Jinsha River - Ailao Mountain alkali-rich porphyry metallogenetic belt, is one of the typical gold-polymetallic metallogenesis system related to alkali-rich intrusion during the Himalayan epoch. Based on the previous researches and the extensive field investigations from the recent scientific programs, this article systematically studies the petrogenesis, metallogenesis evolving sequence in the ore district and their responses to the Indo-Asian collisional processes. The main intrusion rock types including quartz-albite porphyry, quartz-K-feldspar porphyry and biotite-K-feldspar porphyry with adakitic magma affinity, which intruded during the period of 65 to 59 Ma, 36 to 32 Ma, 26 to 24 Ma and 3.8 to 3.6 Ma respectively. The magmas of ore-bearing alkali-rich porphyries were derived from mixed melting of the crust-mantle transitional layer in eastern margins of the Tibet plateau, and genetically related to the asthemosphere eastern-extruding and the large-scale strike-slip faulting due to the Himalayanian Indo-Asian collisional systems. The duration of the first episode and the second episode are consisted with the two concentrative petrogenesis episodes approximately. Within the ore district, three types and seven subclasses of gold-polymetallic deposits have been recognized, there are (I) porphyry copper-gold-polymetallic deposits related to the first and second stage of alkali-rich porphyry intrusion, including skarn-type gold-polymetallic deposits (including magma-type), porphyry-type copper-gold deposits and hydrothermal-type gold-polymetallic deposits, (II) porphyry-related hydrothermal-type gold-polymetallic deposits due to the third stage of alkali-rich porphyry intrusion, including cryptoexplosive breccia-type gold-ferrous -lead- zinc-polymetallic deposits and hydrothermal superimposed-type gold-polymetallic deposits, and (III) weathered-sedimentary-type deposits associated with the fluvial and lacustrine sedimentary rocks formed by the surface weathering and the laterization, including red clay-type gold deposits and palaeoplacer-type gold deposits. The I- and II-type deposits were controlled directly by the alkali-rich porphyry intrusion and NE-NNE-trending strike-slip faulting, and occur in the porphyry intrusions, the cryptoexplosive breccia pipes, the porphyry contacts and the porphyry outside contacts of the fractured zone and the intensive joint zone within middle Triassic limestone of Beiya Formation. The earlier deposits usually were overprinted by the later epithermal mineralization system associated with late magmatism, which formed either isolated, but spatially coexisted a high-grade giant deposit, and all provided the material sources for the palaeoplacer-type deposits. Correspondingly, ore-forming mineralization also changed from Cu-Au-(Mo) associations, Fe-Cu-Au-Pb-Zn associations to Au-Pb-Zn-Ag associations, the mineralization resources and fluid resources both come from the alkali-rich porphyries magmatism, and construct a porphyryhydrothermal metallogenic system, the wall rocks only provide a space for the metal deposition. The secondary enrichment and supergenetic mineralization began at the time of the primary gold deposits occurrence, and brought up various weathered-sedimentary-type deposits.
Among them, the palaeo red clay-type gold deposits formed during the period from Eocene to Oligocene, the palaeoplacer gold deposits formed during the period rom 23 to 5 Ma, and the modern red clay-type ( including eluvium-type) gold deposits continued all along. Comparing to the regional evolution sequences, it is explained that the Beiya gold-polymetallic deposits be controlled by the evolution of the Indo-Asian collisional orogen and tectonomagmatism under the collision belt, which implies the same dynamic setting of paroxysmal mineralization of porphyry-type deposits to the eastern Xizang-Jinsha River-Ailao Mountain porphyry metallogenetic belt, displayed the long-distance effects in the structural transform zone of the main collisional orogenic setting since the Palaeocene. Episodically stress relaxation during tectonically transforming from transpressional(55 similar to 40 Ma) to transtensional (24 similar to 17 Ma) regimes probably caused multiple magmatic intrusions, which most likely result in the protraction of the hydrothermal system and superimprosed mineralization in the eastern Indo-Asian continental collision zone, and the duration from 36 to 32Ma is the main mineralization period of the porphyry- hydrothermal metallogenic system. There are great gold-polymetallic prospective reserves within the deep areas of ore district and surrounding regions. It is possible that the Yanyuan-Lijiang fault control a comparatively independent porphyry metallogenetic belt with close relationship to the Xizang-Jinsha River - Ailao Mountain porphyry metallogenetic belt.
- 出版日期2008-3
- 单位昆明理工大学; 中国地质科学院
