云南有色金属地质调查局范茂煌研究组近日取得一项新成果。他们报道了云南东南白牛场花岗斑岩地球化学及U-Pb年代学。相关论文发表在2025年1月20日出版的《地球化学学报》杂志上。

研究人员表示，白牛场银多金属矿床位于中国云南省东南部，是该地区最大的矿床之一。然而，该矿区的浅浅花岗岩斑岩尚未得到全面调查。

本文对白牛场花岗岩斑岩样品进行了地球化学、年代学、全岩Sr-Nd同位素和锆石Hf同位素分析。结果表明，该花岗斑岩形成于燕山晚期87.5 ~ 87.4 Ma。地球化学特征表明，花岗岩为强过铝质花岗岩，硅、碱含量高，符合s型花岗岩特征。花岗斑岩富集大离子亲石元素（Rb、Th、U、K），Ba和Sr相对贫乏。初始87Sr/86Sr比值较高（0.71392 ~ 0.71585），εNd(t)值较低(8.9 - 8.2)。锆石表现出相似的低εHf(t)值。

这些数据表明，形成斑岩的岩浆起源于大陆的岩浆源。两阶段Hf和Nd模式年龄分别为1534 ~ 1216Ma和1615 ~ 1561Ma。其中，花岗斑岩可能形成于燕山晚期走滑伸展背景下，是元古代基底变质岩重熔的产物。该斑岩与矿床内隐伏的花岗岩体具有相似的岩浆成因，与燕山期构造活化有关。研究结果为研究白牛场地区构造岩浆成矿过程，提供了有价值的认识。

附：英文原文

Title: Geochemistry and U–Pb geochronology of the granite porphyry in Bainiuchang, Southeastern Yunnan, China

Author: Shi, Nan, Zhu, Jun, Liu, Xuelong, Zhang, Shitao, Meng, Guangzhi, Zhang, Hong, Cheng, Jialong, Zhou, Jiehu, Lu, Bode, Dao, Junshan, Mi, Xue, Fan, Maohuang

Issue&Volume: 2025-01-20

Abstract: The Bainiuchang Ag-polymetallic ore deposit, located in southeastern Yunnan, China, is one of the region’s largest deposits. However, the hypabyssal granite porphyry within this mining area has yet to be comprehensively investigated. In this study, we conducted geochemical, geochronological, whole-rock Sr–Nd isotope, and zircon Hf isotope analyses on granite porphyry samples collected from the Bainiuchang deposit. The results indicate that the granite porphyry formed between 87.5 and 87.4 Ma in the Late Yanshanian period. Geochemically, the granite is strongly peraluminous, with high silica and alkali contents consistent with S-type granite characteristics. The granite porphyry is enriched in large-ion lithophile elements (Rb, Th, U, and K) and is relatively depleted in Ba and Sr. The initial 87Sr/86Sr ratios are high (0.71392–0.71585), accompanied by low εNd(t) values (8.9 to 8.2). The zircons exhibited similarly low εHf(t) values (9.31 to 3.6). These data suggest that the porphyry-forming magma originated from a continental crustal source. The two-stage Hf and Nd model ages are estimated at 1534–1216 Ma and 1615–1561 Ma, respectively. Thus, the granite porphyry likely formed under a strike-slip extensional setting in the Late Yanshanian period and resulted from the re-melting of Proterozoic basement metagreywackes. This porphyry shares a similar magmatic origin with concealed granite bodies within the deposit and is associated with structural reactivation during the Yanshanian. The findings of this study provide valuable insights into the tectonomagmatic mineralization processes in the Bainiuchang area.

DOI: 10.1007/s11631-024-00750-x

Source: https://link.springer.com/article/10.1007/s11631-024-00750-x