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Padaeng
Thailand
Main commodities: Zn Pb


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The Padaeng supergene non-sulphide zinc deposit is located near Mae Sod in Tak province, north-west Thailand close to the Myanma (Burmese) border.

Padaeng lies within the Shan-Thai (or Sibumasu) terrane which extends from Yunnan (China) in the north, through Myanmar and Thailand to Peninsula Malaysia and Sumatra (Indonesia).   Padaeng is hosted by a marine middle Jurassic sequence (which includes significant carbonates) that unconformably overlie Permo-Triassic clastics, carbonates and volcanics that have been subjected to lower greenschist facies metamorphism during the Triassic and intruded by late orogenic Triassic batholithic granitoids to the east.   These are part of regional north-south trending synform that extends 200 km from north to south through Mae Sod.   This is part of the same carbonate basin as the Kanchanaburi deposits to the south.

The host Jurassic carbonates are characterised by interbedded mixed clastics and carbonates, and in the Paedang area comprises a lower 140 m of basal limestone conglomerate, the Khun Huai Formation lying unconformably on the Triassic, and overlian by limestones, marls and interbedded mudstone.   These are followed by a 370 m thick mudstone and interbedded limestone unit with lenses of cross bedded sandstone, the Doi Yot Formation, ovelain in turn by a third unit, the Pha De Formation, composed of limestone-marl with minor mudstone and oncolitic beds.

At Paedang a thinned Khun Huai Formation unconformably overlies Triassic basement, and is followed by the mineralised Doi Yot Formation.   Zinc mineralisation is hosted by dolostone, weathered dolomitic sandstone and sandy dolostone, bounded to the south by the NE dipping Paedang Fault.   The local stratigraphy comprises from the base:
i). Lower Limestone - a black argillaceous to shaley limestone and oncolitic, fossiliferous micritic wackestone,
ii). Pit Limestone - thick bedded, fine grained, silty limestone with minor sandy oolitic and bioclastic argillaceous beds, all pervasively replaced by dolomite in the mine area,
iii). Pit Sandstone - cross bedded calcareous sandstone, oolitic sandy limestone and minor argillaceous bioclastic limestone, all pervasively dolomitised in the mine area,
iv). Crystalline Dolomite - medium to coarsely crystalline hydrothermal dolomite, commonly vuggy,
v). Upper Bioclastic Limestone - including oolitic bioclastic, argillaceous limestone at the base passing up into oncolitic and bioclastic, micritic wackestone and packstone with thin argillaceous interbeds.

High grade non-sulphide zinc is hosted by the Pit Sandstone and Crystalline Dolomites in the footwall of the East Pit Fault.   The original pre-mining mineralisation at surface occured as an outcropping blanket on the NW facing dip slope and had grades of up to 30 to 40% Zn.   To the west hemimorphite dominated, while to the east smithsonite was the main oxide mineral, passing down at depth to hemimorphite.   The base of mineralisation was very erratic.   Three dominant ore geometries are delineated, as follows:
1). the dominant ore type, stratabound lenses mainly in the Pit Sandstone, almost all within the coarse grained sandstones, but also occuring in sandy units in the underlying Pit Limestone.   Hemimorphite occurs as secondary cement within the weathered sandstones, as network veinlets or as semi-massive botryoidal replacements.   Mineralisation occurs to depths of more than 180 m.   No significant sulphides are found down dip of the supergene ore.
2). steeply dipping linear NNW to NNE trending mineralised zones, within the Pit Sandstone, below the stratabound ores in steeply dipping karst structures controlled by fractures and composed of hemimorphite, and
3). irregular karstic zones in the Pit Limestone.
Some 100 m to the north a fourth style comprises high grade smithsonite capping low grade sphalerite mineralisation in the Crystalline Dolomite.

Sulphide deposits of zinc-lead are known in the surrounding district, the largest being Pha De, which is 2.4 km to the NW with 0.43 Mt @ 15% Zn, 1.5% Pb.

Pre-mining reserves at Padaeng in 1984 were:   4.59 Mt @ 28.9% Zn at a 10% Zn cut-off.
Production 1984 to 2002:   4.8 Mt @ 20% Zn
Resources in 2003 are:   5.14 Mt @ 12.0% Zn at a 3% Zn cut-off.

For detail consult the reference(s) listed below.

The most recent source geological information used to prepare this decription was dated: 2003.    
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
   Selected References:
Reynolds N A, Chisnall T W, Kaewsang K, Keesaneyabutr C, Taksavasu T  2003 - The Padaeng supergene nonsulfide zinc deposit, Mae Sod, Thailand: in    Econ. Geol.   v98 pp 773-785


Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge.   It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published.   While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo, its employees and servants:   i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and   ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.

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