Sichuan, China

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The Lala iron-copper deposits Luodang, Huidong and Shilong, are located within the Kangdian iron oxide copper-gold (IOCG) metallogenic province, in Sichuan Province, SW China, ~150 km NNW of Kunming and 120 km west of Donchuan (#Location: 26° 6'N, 101° 57'E).

The Kangdian metallogenic province extends for ~300 km adjacent to the southwestern margin of the Yangtze block. The Yangtze Block occupies the northwestern half of the South China craton, and is bounded to the SE by the Cathaysia block (the other half of the craton), to the SW, across the Red River fault, by the Indochina craton, and to the west by the much younger Tibetan plateau.

There are more than 50 iron and or copper deposits in the Kangdian IOCG province, accounting for 21% of the high-grade Fe resources in China (Sun et al., 1991). In addition to Lala, other relatively large deposits in the province include the Dongchuan, Yinachang and Dahongshan deposits (Zhao and Zhou, 2011) which are hosted in the Palaeoproterozoic Hekou, Dongchuan and Dahongshan Groups. The Dongchuan deposits are either Cu sulphide, or Fe-oxide-(Cu) dominated (Qian and Shen, 1990; Ruan et al., 1991; Zhao, 2010). Cu sulphide-dominated orebodies typically occur in the dolostone of the Dongchuan Group and were classified as sediment-hosted stratabound copper-type deposits (Zhao, 2010; Zhao et al., 2012). Fe-oxide-(Cu) dominated orebodies contain abundant Fe oxide with or without Cu sulphides, and are specifically hosted in metavolcanic rocks of the Dongchuan Group (Chen and Zhou, 1999). Zhao and Zhou (2011) regard these deposits as comparable to IOCG deposits elsewhere in the world.

Sparse ~2.9 Ga rocks are exposed in the northern part of the Yangtze block (Gao et al., 2001), while abundant ancient lower crustal xenoliths (Zheng et al., 2006) and Archaean to Palaeoproterozoic detrital zircon found in Meso- to Neoproterozoic sedimentary sequences elsewhere in the block (Sun et al., 2009; Zhao et al., 2010) suggest widespread Archaean to Palaeoproterozoic basement rocks. Widely distributed inliers of Proterozoic rocks within the block are thought to be folded basement, which are unconformably overlain by an unmetamorphosed Neoproterozoic-Sinian to Cenozoic cover sequence (Yan et al., 2003)

Proterozoic volcano-sedimentary sequences define a north-south belt within the western Yangtze block, extending for ~500 km from Kangding (Sichuan Province) to Yuanjiang (Yunnan Province). These sequences include the late Palaeoproterozoic Hekou, Dahongshan and Dongchuan Groups, and the Meso- to Neoproterozoic Huili, Kunyang, Julin and Yanbian Groups (Chen and Chen, 1987; Li et al., 1988). The Dahongshan and Dongchuan Groups contain ~1700 Ma (zircon U-Pb ages) volcanic layers (Hu et al., 1991; Greentree and Li, 2008; Zhao et al., 2010), whereas the Mesoproterozoic Kunyang Group contains ~1100 Ma (zircon U-Pb ages) volcanic units (Greentree et al., 2006; Sun et al., 2009), roughly coeval with the Huili Group (Greentree et al., 2006; Geng et al., 2007). The Neoproterozoic Yanbian Group contains detrital zircon grains as young as ~850 Ma (Zhou et al., 2006; Sun et al., 2009). The Palaeoproterozoic Hekou Group and its equivalents were metamorphosed to upper greenschist-lower amphibolite facies (Li et al., 1988), whereas the younger Kunyang, Huili, and Yanbian Groups were only subjected to lower greenschist facies metamorphism (Chen and Chen, 1987; Li et al., 1988). Metamorphism was most likely from 900 to 750 (e.g., Zhao and Zhou, 2011), but may have been from 1300 to 1000 Ma (Li et al., 2003). The Proterozoic sequences are intruded by numerous Meso- to Neoproterozoic plutons. Magmatism of the latter phase produced ~860 to ~740 Ma granitic, dioritic, and gabbroic intrusions (Zhou et al., 2002, 2006; Li et al., 2003; Zhao et al., 2008), variously interpreted to be arc (Zhou et al., 2002, 2006; Zhao and Zhou, 2007) or mantle plume related (Li et al., 2003). Lesser ~1100 Ma gabbroic intrusions of are predominantly found in the Dongchuan and Dahongshan areas, displaying intraplate magmatism geochemical affinities.

The Lala group of Fe-Cu deposit is hosted in the Hekou Group that is in fault contact with the Huili Group to the W and NE and is unconformably overlain by Neoproterozoic-Sinian and Phanerozoic strata to the NW and E-SE. From the base upward, the >1800 m thick Hekou Group, which has a roughly SE-NW striking and SW dipping metamorphic foliation comprises (cf. Zhou, 2005) the:
  Dayingshan Formation, composed of a lower rhythmically layered, magnetite-bearing quartzite, slate, schist and phyllite with local marble lenses, overlain by K-feldspar-quartz albitite with interlayers of porphyritic quartz albitite and schist in its uppermost parts;
  Luodang Formation, predominantly garnet-biotite schist and black slate at the base, with rhythmic interbeds of massive quartz albitite, metatuffaceous sandstone and garnet-mica schist at the top, with local lenses of siderite marble; and
  Changchong Formation, which contains rhythmic interbeds of metasandstone, schist and marble in the lower parts, and interbeds of quartz albitite, schist and marble at the top.
Gabbroic intrusions, and lamprophyre and felsic dykes intrude the Hekou Group. Close to orebodies, rocks of the gabbroic intrusions are strongly altered to chlorite, actinolite, albite and magnetite, and they are also commonly crosscut by abundant calcite-quartz-hematite veins, although their ophitic texture and minor primary clinopyroxene are still preserved. The lamprophyre and felsic dykes are scattered throughout the mining fields and occur mainly along faults. The gabbroic intrusions have well-developed foliations parallel and similar to that of the Hekou Group, while most of lamprophyre and felsic dykes are undeformed, and locally intrude orebodies (Zhou, 2005).

The Lala Fe-Cu deposits include, from west to east, Luodang, Huidong and Shilong. These orebodies are all hosted by albitite, mica-schist and minor quartzite in the upper part of the Luodang Formation of the Hekou Group. Orebodies predominantly occur as irregular lenses and veins and are roughly stratabound, striking NW-SE and dipping to the south. They are structurally controlled and mainly confined to NW-SE striking and SW dipping foliations. Several bodies are also controlled by east-west striking lithologic contacts, faults, or shear zones. Following mineralisation, both the host rocks and ore were folded along north-south trending axes and truncated by younger, steeply dipping, north-south faults (Chen and Zhou, 2012).

The deposits are both complex and heterogeneous with iron and copper occurring either separately or together as: i). oxides, as massive to disseminated magnetite, and stringers and bands of magnetite following foliation planes; ii). sulphides, occurring as bands and stringers parallel to foliation planes, or as disseminations, as well as stockworks and massive veins or discontinuous veinlets of sulphides, crosscutting the foliation of host rocks and oxide ores; iii). mixed oxide-sulphide ores, where sulphide minerals occur either pervasively, or as banded replacements and veinlets, overprinting earlier banded and disseminated magnetite (Chen and Zhou, 2012).

Local breccias within the Lala deposits are generally associated with orebodies, occurring either as <10 x 2 m zones roughly parallel to lithologic contacts, or as irregular bodies <3m wide. Clasts within the breccias are subrounded to angular with variable sizes, and include albitite, marble, gabbro and minerals such as quartz and calcite. They are strongly altered, with some completely replaced by K feldspar or calcite. The breccia matrix is comprises variable proportions of hydrothermal minerals including K feldspar, calcite, quartz, chlorite, biotite, sulphide minerals and magnetite. Most breccias are deformed and fragments are commonly elongated, predating metamorphism, although some minor breccias contain clasts of foliated albitite, schist and magnetite-rich mineralisation, possibly postdating the metamorphism (Zhou, 2005).

The paragenetic sequence at these deposits includes metamorphosed (I, II and III) and unmetamorphosed (IV and V) stages. Stage I comprises extensive, pervasive sodic alteration, forming abundant albite, but only minor scapolite; Stage II takes the form of massive and banded replacements, of Ti-V-poor magnetite and apatite with minor disseminated sulphide minerals, and was associated with pervasive K-Fe alterations producing K feldspar, chlorite and actinolite. Stage III is predominantly bands and disseminations following foliations, with minor veinlets crosscutting hosting rocks, characterised by abundant Fe-Cu-Mo sulphides intergrown with angular magnetite, and minor titanite and allanite, and associated carbonate, quartz, fluorite and mica alteration; Stage IV produced an assemblage dominated by chalcopyrite with variable pyrite and bornite, occurring as veins of sulphides + quartz + calcite + biotite ± muscovite ± fluorite; Stage V is chiefly present as veins of hematite ± calcite ± quartz and extensive hematisation (Chen and Zhou, 2012).

Stage II and III have fluids with high δ18O (7.2 to 11.7‰) and δ34S values (0 to 4‰), indicative of a magmatic-hydrothermal origin. In contrast, the stage III fluids have δ34C values (~0.5‰) close to the least altered marble (0 to 2‰) of the host rocks, indicating a possible contribution of sediment-sourced carbon. The stage IV fluids have δ34C values similar to and δ18O (4.1 to 6.7‰) lower than the stage III fluids, and a wider range of δ34S values (-9.0 to +10.5‰), consistent with significant contributions of sediment-sourced sulphur. Fluids of the late barren vein stage (V) have relatively low δ34C (-4.0 to -2.4‰) and δ18O values (-2.9 to +0.6‰), indicative of significant contributions of meteoric and oxidised fluids. Molybdenite from stage III has an Re-Os isotope age of 1086±8 Ma, providing tight constraints on the timing of the main stage of mineralisation. This age suggests that the Lala deposits are coeval with the ~1100 Ma intraplate magmatism in the western Yangtze Block (Chen and Zhou, 2012).

The Luodang deposit is exploited by open-pit and Huidong and Shilong by underground mining.

The three deposits contains more than 200 Mt @ 13 wt.% Fe, 0.92 wt.% Cu (Chen and Zhou, 2012).

The most recent source geological information used to prepare this summary was dated: 2012.    
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd.   Unauthorised copying, reproduction, storage or dissemination prohibited.

  References & Additional Information
 References to this deposit in the PGC Literature Collection:
Chen W T and Zhou M-F  2012 - Paragenesis, Stable Isotopes, and Molybdenite Re-Os Isotope Age of the Lala Iron-Copper Deposit, Southwest China : in    Econ. Geol.   v.107 pp. 459-480
Zhu Z and Sun Y,  2013 - Direct Re-Os Dating Of Chalcopyrite From The Lala IOCG Deposit In The Kangdian Copper Belt, China : in    Econ. Geol.   v.108 pp. 871-882

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