Minerralization Characteristics Of The Hongshui River Iron Deposit, Dulan County, Qinghai Province

The Flood River iron deposit in Dulan County, Qinghai Province is a recently discoveredlarge-scale iron deposit in Qinghai Province. The ore bodies mainly occur in the-grey-greengravel-bearing chlorite phyllite and grey-black calc phyllite in the lower part of the Langyashanformation of Jixian system. The deposit is now under mining, but relatively few studies of metallogenicregularity have been conducted.This paper focun a summary of the first hand geological evidences for mineralization of thedeposit. The following conclusions are obtained:(1) The Flood River iron deposit is tectonically located in southern part of the Central EasternKunlun granite-metamorphic complex uplift belt. The deposit is hosted in a sequence of low grademetamorphic magnesium carbonates and carbonates interlayered with fine-grained clastic rocks in theLangyashan group (JXL) in Middle Proterozoic Jixian system.. The wall rocks of the ore bodies aregravel-bearing chlorite phyllite and grey-black carbonaceous calc phyllite. The lithological sequencesare, from bottom-up, grey-black banded marble and limestone, grey-black biotite phyllite, sericitecalcareous phyllite and interlayered thin-bedded limestone-iron ore layer-grey-green gravel-bearingchlorite phyllite, carbonaceous phyllite interlayered with chlorite phyllite, dolomitic, siliceous marble,carbonaceous phyllite, dolomitic (solidified) marble.(2) The ore-bearing sequence and its roof/floor rocks constitute a transgressive sequence, in whichthe clastic rocks, limestones (marble) form a complete sedimentary cycle. Iron layers are in the lowerpart of the transgressive sequence. The thickness of the ore-bearing sequence is great and the top andbottom marker layers are rather clear. The main ore seam is located between the footwall biotite phylliteand hanging wallgravel-bearing carbonaceous phyllite and chlorite phyllite. In overall the ore-bearingsequence are high in carbon content and regionally stable. The ore bodies are strictly controlled bystratigraphic horizons.(3) The ore bodies are generally of single-layer ore body. The main ore body extends more than3000m along strike. The thickness varies due to different rock facies and deformation. The ore bodystrikes NWW and dips180°to220°with dip angles of60°to75°. The thickness of the ore body isrelatively stable, generally of5to15m with an average of9.3m. Variation of thicknesses along strikeand dip is not very obvious. Locally the ore body is layered-formed, or lens-formed, consistent with thewall rocks. The shapes of the ore bodies changes with the wall rocks due to deformation, being locallytwisted into "S"-shaped. Generally, the shapes of the ore body is relatively stable, but varies with thesedimentary facies along strike and dip. Therefore the ore bodies may be pinch and swell in shapes orform pepper-shapes.(4) Since the major ore mineral is magnetite, the magnetism of the ores is significantly higher thanthe wall rocks. The geomagnetic anomalies, therefore, is significantly in linear distribution.(6) The middle Kunlun deep fault controls the distribution of stratigraphic sequences in the miningarea, which is also in NWW orientation. Secondary NE-trending and nearly north-south trendingstructures control the localization of the ore bodies and may make themdestructed.(7) Magmatic activities in the mining area are not well developed. Some small diorite and syenitedykes are exposed. They locally intrudes the ore bodies, that the latter are destructed, although locallyenriched.