Structural controls on the Lala iron-copper deposit of the Kangdian metallogenic province, southwestern China: Tectonic and metallogenic implications

摘要

The Lala Fe-Cu deposit is a typical iron-oxide copper-gold (IOCG) deposit of the Kangdian region, southwestern China. Structural controls on the orebodies are suggested but not well-understood. Herein, structural analysis is conducted in the Luodang open-pit of the Lala deposit. It reveals that the Lala deposit has undergone multiple deformation events. The D1 stage is the earliest and corresponds to a late Paleoproterozoic rifting, resulting in the Hekou Group (host rock) deposition and the development of bedding-parallel foliation. The D2 event is synmineralization and coincident with an ESE-trending compression. During the D2 compression, the bedding-parallel foliations were preferentially dilated and facilitated ore-forming fluid infiltration, ore replacement and the infilling of bedding-parallel veins. As the compression continues, folding via flexural-slip has enhanced the bedding-parallel veining and, moreover, has induced further dilation along the fold hinges, where "saddle-reef" type ore shoots have been developed. The D3 event represents an ESE-directed extension, which has induced an overprint of the mineralization, characterized by biotite-sulfide veins crosscutting the stratiform ores at high angle. The E-W trending structures, faults and folds probably represent a post-mineralization north-south compression (D4). In combination with previous paragenetic and geochronological studies, the D2 and D3 mineralization is inferred to occur at ca. 1.05 Ga and ca. 0.83 Ga respectively. The timing and corresponding stress regimes of the deformation events are more consistent with a tectonic model that suggests the late-Mesoproterozoic to early Neoproterozoic (1.05Ga-0.85Ga) Yangtze block is in the process of amalgamation with the Cathaysia and in favor of horizontal compression, whereas the post-0.85 Ga Yangtze is dominated by rifting and extensional stress regime, with possible links to the Rodinia breakup. Structural interpretation of the Lala deposit demonstrates that (1) bedding-parallel shearing, (2) transitional ductile-brittle condition and (3) mildly elevated fluid pressure are the essential factors corresponding to the development of strata-bound replacement-style IOCG mineralization and carries implications for other comparable IOCG deposits.