Structural Controls On The Lala Iron-copper Deposit And Constraints Of Microstructure Characteristics

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 EW-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 EW-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,whereasthe post-0.85 Ga Yangtze is dominated by rifting and extensional stress regime,with possible links to the Rodinia breakup.Through the study of the microstructure characteristics of the samples,based on the microstructural and cutting relations between the foliations,the period of deformation of the stratum in the study area was divided into four stages from the microscopic point of view.The characteristics of the d1 microstructural features in the thinsection are mainly the primary bedding(S0)and bedding-parallel foliation(S1).The d2 stage is mainly characterized by the foliation(S2)which cutting S0 and S1,the microfractures parallel to the bedding,and the ductile shear zone developing along the strata.The d3 microstructures are mainly the subvertical veins(V3)and microfracturing of the normal fault.The d4 stage microstructures are mainly cleavage(S4)and brittle shear bands that cut calcite veins(V3).The microscopic structural features have further confirmed the macroscopical division of the formation deformation stage in the Luodang open-pit.