Lithological and structural controls on gold mineralization in the Archaean Menzies-Kambalda area, Western Australia
Titel:
Lithological and structural controls on gold mineralization in the Archaean Menzies-Kambalda area, Western Australia
Auteur:
Witt, W. K.
Verschenen in:
Australian journal of earth sciences
Paginering:
Jaargang 40 (1993) nr. 1 pagina's 65-86
Jaar:
1993-02
Inhoud:
Structurally controlled gold mineralization in the Menzies-Kambalda area of the Archaean Yilgarn Craton occurs in a wide variety of host rocks and structural settings. The dominant host rocks are Fe-enriched basalt, and fractionated zones of mafic to ultramafic sills. However, other lithologies, including sedimentary and ultramafic rocks, are important host rocks in some mining camps and structural settings. Mineralization occurs in regional shear zones, subsidiary splay structures adjacent to regional shear zones, and in large low strain domains between regional shear zones. The character of the mineralized structures is diverse, ranging from simple quartz veins, through complex vein/breccia systems, to brittle-ductile shear zones. Relatively brittle structures, such as veins and vein/breccia systems are common in low strain domains where they are generally oriented at a high angle to regional structural trends. Mineralization in regional shear zones is more commonly associated with brittle-ductile shears which are conformable within the regional structural fabric. In greenschist and lower amphibolite fades metamorphic rocks, quartz veining and brecciation postdate ductile fabrics within many tabular mineralized brittle-ductile shears. In higher metamorphic grade rocks, mineralization occurs in pipe-like ore shoots, colinear with stretching lineations, within banded ('cherty') shear zones. The regular banded nature of these siliceous high strain zones suggests that quartz veins have been deformed and recrystallized during intense ductile deformation. Mineralized structures can generally be related to the latest events in the regional deformation history of the greenstone belt or forceful emplacement of contemporaneous granitoid intrusions. The latest structural events involve complex, multiple movements on regional shear zones, including sinistral strike-slip faulting, subvertical movements, and oblique dextral faulting, all of which post-date regional folding (D2). Textural evidence from mineralized structures and associated metasomatized host rock assemblages indicate that auriferous fluids were introduced during deformation, and that high fluid pressures actively contributed to the deformation.
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