Magnetic Structure Characteristics and Metallogenic Significance for the Deep Layer of Shilong Copper–Iron Deposit Based on Improved Re-Weighting Regularized Focusing Inversion

The “Lala-type” copper-iron deposits in the Lala area are primarily located in the central part of the Kangdian tectonic zone, distributed along an East-West (EW) trending Neoproterozoic gabbro-dolerite belt that is prominently controlled by regional EW-oriented tectonic structures. The genesis of these deposits is widely believed to be closely related to ancient volcanic structures, but their relationship with deep-seated basic intrusive rocks remains highly controversial. This article proposes an improved 3-D re-weighting regularized conjugate gradient (RRCG) focusing inversion method, constrained by the background field to recover the anomaly with a high resolution. The magnetic structure in a real case indicates the presence of a distinctly oriented basic intrusive rock mass in the deep part of the “Lala-type” Shilong copper deposit. Large-scale, high-precision magnetic profiles and magnetotelluric inversion results show that this strongly magnetic and high-resistance intrusive rock mass, which extends to a depth of 1.5 km, has transformed the ore-bearing basement into a clearly imaged anticlinal uplift and fold structure. Trenches and drill holes reveal that the ore bodies are primarily located in the fold and detachment spaces formed at the intersections of EW and North-South (NS) faults. The breccia formed by the basic rock intrusion along the faults provides favorable conditions for the occurrence and enrichment of ore bodies. The multiple intrusive thermal events in the Lala area not only supplied the fluids necessary for the enrichment of the deposits but also facilitated the transformation of the basement and the formation of ore-bearing spaces.