Intrusion-related Lang Vai gold-antimony district (Northeastern Vietnam): Geology, mineralogy, geochemistry and Ar-40/Ar-39 age

摘要

The Lo Gam domain is one of the most important areas for metallogenic studies in northeastern Vietnam. The Lo Gam domain comprises numerous Pb-Zn deposits and occurrences, which account for 80% of the Pb and Zn resources in Vietnam. Furthermore, within the Lo Gam domain, there are several gold, antimony, and base metal deposits. The largest of these are the Lang Vai, Khoun Puc, and Lung Luong deposits, which are included in the Lang Vai ore district. Each of the deposits includes several ore zones and ore bodies with peculiar mineral compositions and geochemical features. The geological and structural settings show that the Khoun Puc, Lang Vai, and Lung Luong deposits represent a uniform ore system. The metal zoning in the Lang Vai district occurs laterally away from a granitic intrusion. A general paragenetic sequence for the three deposits may be represented by the following mineral associations (from early to late): (i) arsenopyrite, pyrite, native gold, sphalerite; (ii) Bi-rich Pb-Sb sulfosalts; (iii) Bi-poor Pb-Sb sulfosalts; (iv) Sb sulfosalts; (v) Sb-rich minerals, native antimony; and (vi) Pb-rich Sb sulfosalts (as a distal mineral association). Among the different types of mineralizations, there is exists a transient mineralization that is characterized by a complex mineral composition. Bi-bearing minerals have been found only in the Khoun Puc deposit, which is located near a granite stock, whereas Bi mineralization is absent away from the deposit. The general outward sequence of zoning is from Au-As-Bi to Au-As-(Sb) to Sb-(Au-As) to Pb-Sb at the periphery. The ages of mineralization at the Lang Vai and Lung Luong deposits have been estimated to be ca. 240 Ma and ca. 236 Ma, respectively, and are slightly younger than the earlier reported ages (ca. 254-245 Ma) of the Phia Bioc granite complex, indicating a possible genetic relationship between the mineralization and the intrusions. The geological characteristics, metal zoning patterns and new geochronological data suggest that the gold-antimony ores in the Lang Vai district are genetically related to the nearby granitic intrusions.