The nomenclature of carbonate replacement deposits, with emphasis on Sn-F(-Be-Zn) 'wrigglite' skarns
Titel:
The nomenclature of carbonate replacement deposits, with emphasis on Sn-F(-Be-Zn) 'wrigglite' skarns
Auteur:
Kwak, T. A. P. Askins, P. W.
Verschenen in:
Australian journal of earth sciences
Paginering:
Jaargang 28 (1981) nr. 1-2 pagina's 123-136
Jaar:
1981-04
Inhoud:
The nomenclature of replacement deposits is reviewed in terms of two processes, namely those involving the reaction between: (a) carbonate and siliceous rocks and (b) carbonate and unusual solutions, commonly, but not always, related to granitoids. 'Wrigglite' skarn is an example of a replacement deposit produced by process (b). It is highly characteristic rock consisting of alternating light layers of fluorite ± other F-rich minerals and dark layers composed usually of Fe-rich minerals or, rarely, Be-rich minerals. The layers formed parallel or sub-parallel to fractures, which are now veins, by a Leisegang-type diffusion process. Repeated periods of fracturing, with growth away from sequentially produced fractures, produced an apparently chaotic 'wrigglite' skarn. The skarn is invariably enriched in Fe, F, Sn, Be, W, Bi and Zn. For 'wrigglite' to form, fluorine must be greater than 9 weight percent in the rock, and the intrusion of a Sn-leucogranite ('A-type') high into the crust is needed. Recognition of 'wrigglite' is important because (1) in some areas it is an ore of Sn (Mt Bischoff, Tas.), rare earth metals (Bayan Obo, China) or Be (Lost River, Alaska); (2) it indicates a high-level environment of emplacement of a Sn-granitoid; and (3) it indicates clearly that intricate layering can be produced by a diffusional process and not only by primary sedimentation.
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