Earth Science Frontiers ›› 2021, Vol. 28 ›› Issue (3): 112-127.DOI: 10.13745/j.esf.sf.2021.1.8

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Primary halo zonation in and a deep orebody prediction model for the inner-outer contact zone of the Laochang Sn-Cu deposit in Gejiu

ZHU Xu(), YANG Rong, CHEN Yongqing*(), WANG Lianyue, LI Gang   

  1. School of Earth Sciences and Resources, China University of Geosciences(Beijing), Beijing 100083, China
  • Received:2021-01-10 Revised:2021-02-20 Online:2021-05-20 Published:2021-05-23
  • Contact: CHEN Yongqing

Abstract:

The primary haloes of mineral deposits occur as envelopes around individual mineral deposits and are usually contemporaneous with mineral alteration and deposition. Zonation of primary haloes of mineral deposits is quite predictable and explicable, thus it generally provides better ore prospecting targets. Besides, primary haloes of some metal deposits may provide important insight for targeting deeply buried orebodies. The Laochang Sn-polymetallic deposit is an important member of the Gejiu giant (Sn-Cu) polymetallic deposit characterized by skarnized mineralization. The skarnized mineralization can be subdivided into endoskarn and exoskarn mineralization types based on the spatial distribution patterns. The former occurs in the inner altered intrusion zone while the latter mainly in carbonate rocks near intrusions. They have the following geochemical similarities and differences: (1) The axial zoning sequences of endoskarn and exoskarn orebodies are (from head to tail) Ag-As-Bi-Cu-F-Pb-Sn-Zn-B → Ba-Co-Cr-Ni-Sb-V → Be-Mo-W and F-B-Ba-W → Cu-Sb-Be-Cr → Sn-Pb-Zn-Ni-Ag → Co-Mo-Bi-As, respectively, indicating consistency in anomaly element but not in axial zoning sequence. (2) In endoskarn mineralization, there are three ore-forming element associations: (a) As-B-Be-Co-Sn, representing greisenized cassiterite-sulfide-tourmaline mineralization; (b) Ag-Pb-Cu-Zn, representing kerargyrite-galena-sphalerite-chalcopyrite mineralization; and (c) Mo-W, representing skarnized molybdenite-scheelite mineralization. (3) In exoskarn mineralization, there are also three ore-forming element associations: (a) Ag-Bi-Sn-Cu, representing kerargyrite-bismuthinite-stannite(cassiterite)-chalcopyrite mineralization; (b) As-Zn-Pb, representing skarnized arsenopyrite-galena-sphalerite mineralization; and (c) F-Be-W-Mo, representing greisenized fluorite-beryl-scheelite-molybdenite mineralization. The above ore-forming element associations indicate skarn mineralization involves multistage processes. Finally, on the basis of primary halo axial zoning sequence, the prediction patterns of deep orebodies in endoskarn and exoskarn zones are established, thereby providing a powerful tool for the prediction of concealed orebodies.

Key words: pathfinder elements, primary halo zonation, prediction pattern of deep orebodies, Gejiu ore field, SW China

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