We are grateful to Mr. Bryan Yap, President of Lepanto Consolidated Mining Company, for permission to conduct this study in the Mankayan district, for providing access to the air magnetic and radiometric survey results, and for permission to publish the outcome of this study. This work is part of AMIRA Project P765, completed in December, 2006, at CODES, University of Tasmania. The project was sponsored by Anglo American, Anglo Gold Ashanti, Gold Fields, Newcrest, Newmont, Placer Dome, and Teck Cominco, as well as Barrick in the final year, with additional funding provided by the Australian Research Council. We acknowledge the discussion and ideas provided by representatives of the sponsoring companies, and assistance by the AMIRA research coordinator Alan Goode. We thank Lyndon Bradish and Froilan Conde, plus many other Lepanto staff, including Bene, Danny, Ed, Louie, Perfecto, Perry, Ric, and Willy, for their assistance, and Dave Braxton for help in the field. Paddy Waters of Anglo American Philippines generously provided logistic support and funding for some of the whole-rock geochemical analyses. We appreciate the help from CODES staff, including Simon Stephens for sample preparation, Sarah Gilbert and Leonid Danyushevsky for LA-ICP-MS analyses, and June Pongratz for report preparation. We thank Roger Stoffregen for comments on an early version of the manuscript, and John Thompson and Raymond Jannas for useful reviews.

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Detailed b lattice parameter and illite crystallinity (IC) studies of K-white micas in slates from the Stawell and Ballarat-Bendigo Zones (SZ, BBZ) in the western Lachlan Fold Belt of Victoria, Australia, reveal a metamorphic pattern characterized by regional metamorphism associated with crustal thickening and younger contact metamorphism accompanied by deformation. The IC data indicate that rocks regionally metamorphosed prior to the intrusion of the Early and Late Devonian granitoids, vary in grade from epizonal (greenschist facies) to diagenetic (zeolite facies) and that most are of epizonal to anchizonal (prehnite-pumpellyite facies) grade. In the BBZ, a decrease in grade from west to east occurs. Across fault zones, IC values show little change, indicating that limited vertical displacement has occurred. This is in accord with the thin skinned deformation model proposed for the western Lachlan Fold Belt. The b lattice parameters (x=9.022 Å ; n=137; s n =0.009) indicate baric conditions intermediate between those of New Hampshire (P=Al 2 SiO 5 triple point) and Otago (intermediate P ). Thus, a moderately low geothermal gradient existed 450-430 Ma ago, when these rocks were deformed. K D Fe/Mg (actinolite)/Fe/Mg (chlorite) values (0.52-0.70) obtained from coexisting actinolite and chlorite in metabasites from fault zones support the moderately high-P (c. 4 kbar) metamorphism suggested by the b cell parameter values.The metamorphic conditions indicated by these data are contrary to the low-P/high-T conditions proposed by previous authors, who inferred an intimate association between deformation, granitoid intrusion and gold mineralization. The b lattice parameter of white micas in slates adjacent to Early Devonian (c. 400 Ma) granitoids with schist bearing aureoles in the north-eastern part of the BBZ (x=9.002 Å ; n=27; s n =0.007), indicate pressures in the order of c. 2.5 kbar which are in accord with those obtained from andalusite-cordierite and zoisite-garnet bearing assemblages observed in the higher grade metapelitic and calcareous rocks. This contrasts with the higher pressure (c. 4 kbar) existing during regional metamorphism and implies that c. 6.5-8 km of metasedimentary rocks in the BBZ were removed before the emplacement of the Early Devonian granitoids. Metamorphic assemblages in hornfelses associated with Late Devonian granitoids indicate a further 5-6 km of metasediment were removed in the next 40 Ma prior to their emplacement. This study shows the value of white mica studies in elucidating the tectonothermal history of a low-grade metamorphic terrane dominated by metapelitic rocks.