Journal of Petrology Volume 41 Number 2 Pages 305-306 2000
© Oxford University Press 2000
BOOK REVIEW |
Mineralized Intrusion-Related Skarn Systems, edited by D. R. Lentz. Short Courses Volume 26. Mineralogical Association of Canada, Ottawa, Ont., 1998. 664 pp. ISBN 0921294263. US$48.
University of Leeds
Despite masquerading under the title of a Short Course volume, this book is anything but short and, I suspect, bears little relation to original course material; it is a substantive monograph on skarns. There are a number of general chapters but the main emphasis is on case studies, with a good balance of economic and genetic aspects.
Of the general chapters, Bowman’s account of phase equilibria in simple skarn systems provides a clear exposition of the basic equilibrium phase relationships, and goes on to show how phase equilibria can buffer fluid phase activities, using log activity diagrams. This sort of material is not well covered in most books, and so is particularly useful. In contrast, the chapter by Burt on the vector treatment of mineral compositions actually includes an acknowledgement to the editor for ’asking me to write this material up yet again’. Bowman also contributes a chapter dealing with C–H–O–S stable isotope systematics in skarn systems. Starting from a simple beginning, this chapter leads through each of the major stable isotope systems, and shows how they can be used singly or in combination to track reservoirs of materials involved in skarn production, and to monitor fluid flow processes.
Although an understanding of equilibrium relationships is an essential prerequisite to investigating the complexities of skarn formation, it is apparent to anyone who has ever studied a BSEM image of zoning in skarn minerals (and you will look for one in vain in this book) that irreversible processes play a fundamental role in their genesis. Such processes that lead to the formation of skarns are only now beginning to be analysed, and the chapter by Dipple and Gerdes on reaction–infiltration feedback and hydrodynamics at the skarn front is a welcome attempt to address aspects of both geochemistry and fluid flow in an integrated manner.
Two further general chapters deal with the use of mineral chemistry to distinguish different skarn environments. Nakano shows that pyroxene chemistry in proximal Cu–Fe skarns reflects a stronger magmatic component than in Pb–Zn skarns, and Pan provides a wide-ranging review of scapolite chemistry and stability, and shows how the mineral can act as an indicator for P–T conditions, and fluid chemistry, based on both its elemental and isotopic composition.
The remaining 75% of the volume is primarily concerned with case studies of particular types of deposits or particular localities. Keith and coworkers evaluate the contribution of mafic alkaline magmas to the formation of felsic porphyry mineralization, and conclude that they are particularly important for metal concentration processes. A series of exploration criteria are proposed in the light of this conclusion. Newberry updates ideas on Sn and W skarns in the light of current ideas about granite genesis, as well as providing a synthesis of their characteristics. Megaw reviews carbonate-hosted Pb–Zn–Ag–Cu–Au replacement deposits, Meinert summarizes the characteristics of gold-bearing skarns (defined in economic terms), and Birkett and Sinclair review rare metal replacement deposits linked to alkalic magmatism.
Other case studies are of particular districts or regions. Rubin and Kyle provide an excellent review of the Ertsberg East skarn complex of Irian Jaya in Indonesia, which encompasses the geology of the region and the history of exploration of the deposit as well as presenting maps, sections, mineralogical and chemical data. It is concluded that the sulphide mineralization formed late in the development of the skarn, and was sourced from a related intrusion at depth, rather than the exposed body. The Au-skarn at Copper Canyon, Nevada, is described from a geochemical viewpoint by Kotlyar and coworkers, who describe patterns of element zonation and discuss the implications of the apparently small volume of parental granodiorite for the size of ore body. The mineralized skarns of the Canadian cordillera as a whole are reviewed by Ray and Dawson, whose summary classifies and presents statistics for a wide range of skarn deposits, discusses their settings and comments on their origin. The final chapter, by the volume’s editor, Lentz, is, ironically, still essentially unedited. It occupies over a fifth of the book and meanders around a range of topics dear to his heart, with literature review, date and opinion inextricably intertwined. The main thesis is that there is still a place for limestone syntexis in models for the origin of some types of carbonatite magmatic activity, and it would be nice to see the case presented in a more structured and focused manner.
Overall, this is undoubtedly a valuable review volume on skarns with a wealth of detailed information on a wide range of occurrences. Its failure to address the nature of skarn-forming processes in any depth highlights the current limits to skarn research, and should stimulate further work. However, I also found a lot of interesting material here of wider significance, and I believe that the volume deserves to be read by a wider petrologic community than just skarn specialists.
CiteULike 
Connotea 
Del.icio.us What's this?
| ||||||||||||||||||||||||||||||||||||||||||||||||