矿床地球化学国家重点实验室知识库

A number of Proterozoic Fe-(Cu) deposits or prospects are distributed along the Ailao Shan–Red River shear zone (ASRR) in South Yunnan, China and northern Vietnam, defining the potentially important Longbohe–Sin Quyen Fe-Cu belt. This belt was tentatively considered to be initially part of the Proterozoic Kangdian Fe-Cu province in southwestern Yangtze Block (SW China) before being southeastward displaced into the Cenozoic ASRR. However, such a model is still not confirmed convincingly due to poor understanding of ore genesis of the belt and lack of comprehensive comparisons. In this paper, we described the geology and mineralization styles of typical deposits, the Longbohe and Sin Quyen deposits, in the Longbohe–Sin Quyen Fe-Cu belt, and obtained new zircon U-Pb ages of ore-hosting rocks and intruding granites to evaluate if this belt is comparable with the Kangdian Fe-Cu province. Both the Longbohe and Sin Quyen deposits, which are located in northwestern (south Yunnan, China) and southeastern (northern Vietnam) sections of the belt, respectively, are hosted in volcanic-sedimentary rocks that were traditionally named as the Longbohe and Sin Quyen groups, respectively. Both the ores and hosting rocks in the two deposits are variably metamorphosed or deformed, but our results reveal that both deposits have similar paragenetic sequences including pre-ore Na alteration and early Fe-REE mineralization (magnetite and allanite), followed by Cu mineralization (chalcopyrite). Such mineralization styles are broadly comparable to those of the Fe-Cu deposits in the Kangdian province.

Our new zircon U-Pb dating on meta-volcanic and sedimentary rocks of the ore-hosting Longbohe Group and intruding granites indicate that this group consists of at least two parts forming at 1000–750 and ~1700 Ma, and thus is termed as the upper and lower Longbohe groups in this study. On the other hand, the new zircon ages of the ore-hosting Sin Quyen Group and intruding granites tightly constrain the depositional age of this group as 870–830 Ma, broadly synchronous with the upper Longbohe Group. Sedimentary rocks of the upper Longbohe Group contain detrital zircon with ages dominantly clustering at 2.9–2.7, 2.3–2.2, 1.9–1.7, 1.5–1.3 and 1.2–1.05 Ga, broadly similar to those of the Sin Quyen Group, even though the latter also contains an additional spectrum of 1.0–0.87 Ga. In total, these ages of detrital zircon are comparable with those of the synchronous strata in the Kangdian Fe-Cu province, such as the Kunyang, Huili and Yanbian groups. It is also important to note that our newly identified ~1700 Ma lower Longbohe Group is comparable to synchronous strata in the Kangdian Fe-Cu province, such as the 1700 Ma Hekou and Dahongshan groups. Such similarities of ore-hosting rocks in both regions provide robust evidence to support that the Longbohe–Sin Quyen Fe-Cu belt is initially part of the Kangdian Fe-Cu metallogenic province before being displaced into the Cenozoic ASRR shear zone. This new recognition has important implications for regional Fe-Cu exploration particularly in the ASRR shear zone.