|
Ora Banda |
|
|
Western Australia, WA, Australia |
| Main commodities:
Au
|
|
 |
|
|
 |
Super Porphyry Cu and Au
|
IOCG Deposits - 70 papers
|
All papers now Open Access.
Available as Full Text for direct download or on request. |
|
|
The historic Ora Banda Main Lode gold deposits are located near the township of Ora Banda, 65 km north-west of Kalgoorlie in Western Australia. It lies within the Kalgoorlie Terrane of the Eastern Goldfields Superterrane, in the Yilgarn Craton.
Gold was discovered in the Ora Banda area in 1893. The main Ora Banda lodes lie towards the core of a NW-SE elongated 8 x 4 km cluster of gold occurrences and deposits within the brittle-ductile Ora Banda structural zone. It is a zone of high-density faulting and shearing relative to the surrounding area (Tripp, 2000). Strain distribution is heterogeneous, reflected by narrow, tabular high-strain zones separating lithons of essentially undeformed rock. Faults and shear zones cross-cut the stratigraphic sequence and are also localised along rock-unit contacts especially interflow sedimentary rocks (Tripp, 2000). While the trend of the main stratigraphic units is NW-SE, the faulting directions vary from NE-SW to NNE-SSW and east west. The other deposits within this cluster include the Enterprise deposit that is part of the regional Paddington operation.
The Ora Banda lodes are hosted by basalts of the Kalgoorlie greenstone belt on the NE limb of a large SE plunging syncline. These comprise a lower unit of komatiites capped by high magnesian basalts, a thin sequence of pelites and quartz porphyry, then a succession of tholeiitic basalts, the upper porphyritic member of which hosts the Ora Banda lodes. Minor sediments are interbedded with the tholeiites, including a graphitic shale which separates the lower tholeiites from the upper porphyritic basalts. The sequence is cut by substantial (500 to 1800 m thick) layered sills of gabbro, quartz gabbro, peridotite, orthopyroxenite and norite.
The lode system is hosted by narrow dextral shears and massive altered zones which fall into three groups, ENE, east-west and NW, the latter being parallel to the regional strike. The Ora Banda Main Lode strikes ENE, dips at 70 to 80° N, is 1500 m long, persists for at least 500 m down dip and is up to 25 m, but averages 10 to 15 m in thickness. Ore shoots associated with the Main Lode, such as the Victorious and Gimlet, can be up to 50 m wide. The lodes at Ora Banda contain steeply plunging shoots and rod like lenses of fine veins in dilational jogs.
Alteration assemblages include aggregates of sericite, quartz, calcite and chlorite with associated disseminated sulphides (finely disseminated pyrrhotite, which is replaced by pyrite). Gold occurs in microfractures and cavities in pyrite and in grey quartz veins along sphalerite-quartz boundaries, associated with sphalerite enclosed by chalcopyrite and with tellurides.
The district is deeply weathered and lateritised to 40 m in the basalts and to depths of up 80 to 120 m below surface in the lodes. Gold has been mobilised and depleted in the weathered zone and concentrated below the base of oxidation.
Total production from the Main Lode open pit to 1988 was - 1.06 Mt @ 3.2 g/t Au;
Remaining reserve in 1988 were - 0.34 Mt @ 3.54 g/t Au.
Underground sulphide reserve in 1988 - 1.75 Mt @ 5 g/t Au, plus satellite bodies with 1.3 Mt @ 2.5 g/t Au.
For detail consult the reference(s) listed below.
The most recent source geological information used to prepare this decription was dated: 1990.
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.
|
|
|
|
Harrison N, Bailey A, Shaw J D, Petersen G N, Allen C A 1990 - Ora Banda Gold deposits: in Hughes F E (Ed.), 1990 Geology of the Mineral Deposits of Australia & Papua New Guinea The AusIMM, Melbourne Mono 14, v1 pp 389-394
|
|
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.
|
Top | Search Again | PGC Home | Terms & Conditions
|
|
