Abstract:

The Jiaodong Peninsula is one of the most important gold mining districts in China, where gold deposits are typically controlled by the NE-trending fault structure involving mainly the Jiaojia, Sanshandao and Zhaoping fault zones, and secondary fault structure involving the Wangershan and Lingbei faults, etc. Much research has been done in the study area with a focus primarily on the surface and shallow metallogenic sections, not on deep metallogensis and quantitative predictions. The Xincheng gold orefield, consisting of the Xincheng, Qujia and Zhaoxian deposits, is one of the super-large gold deposits in the Jiaodong Peninsula. Owing to the Jiaojia fault zone, the scientific research deep drilling in the Zhaoxian mining zone reached below 2500 m, providing us with an excellent opportunity to study the laws of deep mineralization. In this research, utilizing the short-wave infrared (SWIR) characteristics of altered minerals, together with X-ray fluorescence spectrometry (XRF) and pyrite thermoelectricity analysis, we identified altered rocks and typical gold-bearing pyrite from different ore-forming stages. We then performed SWIR 3D quantitative analysis of the main altered mineral muscovite to reveal its ore prospecting characteristics and identify indicators for other altered minerals in the deposit. The results are: (1) The illite crystallinity and the sericite Al-OH absorption wavelength were higher (≥1.2, ≥2205 nm) near the altered rock-type orebody of the Jiaojia main fault structure and lower (0.2-1.2, 2198-2205 nm) far away from the fault structure. (2) Twenty elements were identified by XRF, and principal component and cluster analyses using these elements revealed certain correlation between the Al-OH absorption peak shift and Al, K, Si content change. (3) The pyrite thermoelectric conductivity types are mainly P-type in the structural altered rocks near the Jiaojia main fault and N-type far away from the main fault. In the Xincheng mining district, the top-to-bottom distribution of conductivity types follows the patterns of N-P→P→P-N→N→N-P→P-N and P-N→N-P for the No. I and V orebodies, respectively; whereas P-type is predominant in the Zhaoxian mining district. The denudation degree is generally between 25% and 50% in both mining districts, therefore there are still good prospects for deep prospecting at below 800 m in the Xincheng or below 1500 m in the Zhaoxian mining districts. On the whole, the metallogenic temperatures are mainly between 180-250 ℃ for P-type or 380-460 ℃ for N-type pyrite, and the orebody spatial distribution trend predicted by 3D interpolation modeling using temperature field is consistent with the prediction by 3D orebody grade model. The comprehensive research method in this paper provides new research ideas for deep mineral resource evaluation. The ideas of integrating multi-dimensional information—such as spectroscopic and geochemical data—and visualization of 3D models can be applied in the construction of quantitative mineral models.

Key words: short-wave infrared spectroscopy (SWIR), X-ray fluorescence spectrometry (XRF), pyrite thermoelectricity, deep prospecting Xincheng gold orefield, Jiaodong Peninsula