The Uranium Mineralization of the Macusani District, Southeast Peru: Mineralogy, Geochemistry, Geochronology and Ore-Genetic Model. By Valeria V. Li A thesis submitted to the Graduate Program in Geological Sciences and Geological Engineering In conformity with requirements for the Degree of Doctor of Philosophy Queen’s University Kingston, Ontario, Canada April 2016 Copyright © Valeria V. Li, 2016 Abstract Uranium mineralization of the Quenamari Meseta, Macusani District, SE Peru, is hosted by peraluminous, sillimanite-andalusite-muscovite-biotite rhyolites of the 12.3 - 6.8 Ma Macusani Formation of the Miocene-Pliocene Quenamari Group. The main ore mineral, meta- autunite, (Ca[(UO2)(PO4)]2(H2O)6-8), occurs in fractures in association with weeksite and hydrous Mn- and Fe-mineraloids. The absence of U4+ minerals, as well as any hydrothermal alteration associated with the U ore, strongly suggests that meta-autunite is the primary U mineral. LA-ICP-MS U-Th-Pa geochronology of the meta-autunite revealed that the main ore- forming events occurred at 69 ka, 130 ka and 314-317 ka, and probably at ca. 103-113 ka, 210 ka and 400 ka, all long after the last magmatic activity in the area. The obtained ages unambiguously relate U ore formation to low-temperature Quaternary processes. The δ18O and δ2H values of the mineralizing fluids, inferred from those of the meta-autunite, range from -21.7 ‰ to –12.2 ‰ and from -181 to -123 ‰, respectively, consistent with ore formation from low- temperature meteoric fluids. The timing of ore formation, as well as the mineralogical and geochemical characteristics of meta-autunite and host rocks, such as REE patterns and alteration assemblages, suggests that U was leached from the glassy matrix of the rhyolites, transported by meteoric waters and precipitated as meta-autunite. The majority of known deposits are located on the upper walls of active fluvial canyons, which suggests that the geomorphological environment that is now focusing groundwater flow was also favourable for meta-autunite precipitation. Meta-autunite probably precipitated through the mixing of low-temperature fluids and interaction of the uranyl ion with Fe- and Mn-mineraloids.Thus, although the Macusani U deposits are volcanic-hosted, they differ radically from documented magmatic-hydrothermal systems. ii Acknowledgements I would like to express my special appreciation to my supervisors Dr. Alan Clark and Dr. Kurt Kyser. Your guidance will be always remembered. I would like to thank sincerely the past and presents members of the Queen’s Facility for Isotope Research, specifically Yulia Uvarova, Paul Alexandre, Evelyne Leduc, Christabel Jean, April Vuletich and Kerry Klassen, who provided critical guidance in the analytical work. I also thank Brian Joy and Alan Grant of Queen’s University, and as Ravi Sidhu of the University of Manitoba, for providing valuable assistance with X-ray diffraction and electron microprobe analyses, respectively. I sincerely thank Don Chipley for providing training and technical assistance with ICP- MS along the way, for assessing P interference on the isotopes of interest and for all the time he spent discussing the results and interpretations of the data with me. It was a pleasure to work together on such a challenging project. The present study was generously funded by Cameco Corp., Macusani Yellowcake Inc. and Vena Resources Inc., and by a Society of Economic Geologists Student Research Grant. I thank many talented industry geologists, particularly David Bent, Walter Cuba, Ted O’Connor, Dan Brisbin and Laurence Stefan for sharing their knowledge and providing logistical support. I would like to express my special gratitude to Dr. Clark for the time he spent supervising this project during my last year in the Graduate School despite his difficult personal circumstances. Dr. Clark showed me a level of scientific curiosity and meticulousness I have not imagined before. iii I thank the staff of the School of Graduate Studies, Writing Centre and Learning Strategies, Ban Righ Centre of Queen’s University. Particularly, I would like to thank Lisa Webb of the Ban Righ Centre and Kim McAuley, Associate Dean of the School of Graduate Studies. Kim McAuley’s guidance, mentoring and support will be always remembered. Last, but not least, I thank my family and friends for constant support. I sincerely thank my parents, my friends Nastia, Claire and Rasine’s family. I am eternally grateful to my husband, Alexey, but most importantly to my daughter, Amy. The birth of my daughter during my years in Graduate School gave me strength and much-needed perspective. iv Table of contents Abstract .......................................................................................................................... ii Acknowledgements ........................................................................................................ iii Table of contents ............................................................................................................. v List of Figures ................................................................................................................ ix List of Tables .............................................................................................................. xvii Chapter 1. Introduction ................................................................................................... 1 1.1. Geographical and geological setting of the Quenamari Meseta ................................. 2 1.2. The Macusani Formation of the Quenamari Meseta .................................................. 4 1.3. Uranium mineralization of the Quenamari Meseta .................................................... 7 1.4. Purpose of this thesis .............................................................................................. 11 1.5. Thesis structure ...................................................................................................... 11 Chapter 2. Methodology ................................................................................................ 19 2.1. Field methods ......................................................................................................... 19 2.2. Mineral identification methods ............................................................................... 19 2.3. Mineral and whole-rock geochemistry .................................................................... 20 2.4. U-series geochronology .......................................................................................... 22 2.5. Light-stable isotope analysis ................................................................................... 26 Chapter 3. The rhyolitic host rocks: stratigraphy, petrography, petrogenesis and v pre-mineralization hydrothermal alteration. ................................................................... 30 3.1. Introduction ............................................................................................................ 30 3.2. Stratigraphy of the Macusani rhyolites.................................................................... 30 3.3. Petrography of unaltered Macusani rhyolites .......................................................... 32 3.4. Hydrolytic alteration of the Macusani rhyolites ...................................................... 33 3.4.1. Greisen association .............................................................................................. 33 3.4.2. Argillic alteration ................................................................................................ 34 3.5. Petrogenesis of the Macusani rhyolites ................................................................... 36 3.6. Conclusions ............................................................................................................ 37 Chapter 4. Uranium mineralization of the Macusani District ......................................... 57 4.1. Introduction ............................................................................................................ 57 4.2. Distribution of U mineralization ............................................................................. 57 4.2.1. Areal distribution and scale of U mineralization .................................................. 57 4.2.2. Stratigraphic distribution of U mineralization ...................................................... 58 4.3. Mineralogy and geochemistry of the U mineralization ............................................ 59 4.3.1. Meta-autunite ...................................................................................................... 61 4.3.1. Weeksite.............................................................................................................. 65 4.4. Conclusions ............................................................................................................ 66 Chapter 5. U-Th-Pa geochronology of U mineralization ................................................ 90 vi 5.1. Introduction ............................................................................................................ 90 5.2. Samples selected for geochronology ....................................................................... 91 5.3. Age Calculations .................................................................................................... 91 5.4. U-series ages of the Macusani U mineralization ..................................................... 93 5.5. Discussion .............................................................................................................