AN ABSTRACT OF THE THESIS OF Brendan M. Laurs for the degree of Master of Science in Geology presented on January 17. 1995. Title: Emerald Mineralization and Amphibolite Wall-Rock Alteration at the Khaltaro Pegmatite-Hydrothermal Vein System. Haramosh Mountains. Northern Pakistan. Redacted for Privacy Abstract approved: John H. Di lles Emeralds form within 0.1 to 1 m thick hydrothermal veins and pegmatites which have intruded amphibolite within layered Proterozoic gneisses in the Nanga Parbat- Haramosh massif. Simply-zoned albite-rich miarolitic pegmatites and hydrothermal veins containing various proportions of massive quartz, albite, tourmaline, muscovite, and beryl are associated with a small >3 m thick heterogeneous leucogranite sill of presumed Tertiary age, which discordantly intrudes the amphibolite and is locally albitized. Emeralds form within thin <30 cm wide massive quartz veins and tourmaline- albite veins, and more rarely in pegmatites, near the contacts with altered amphibolite. Electron microprobe analyses of colorless, pale blue, and emerald green beryl indicate that coloration is due to Cr3+ ± Fe2++Fe34-. Emerald green color is produced by Cr2O3 >0.20 wt%; Fe oxide varies from 0.62 to 0.89 wt% in emerald, 0.10 to 0.63 wt% in pale blue beryl, and 0.07 to 0.28 wt% in colorless beryl. The amphibolite adjacent to the pegmatites/veins is hydrolytically altered into ca. 20 cm-wide symmetrically zoned selvages. A sporadic inner zone containing biotite + tourmaline + fluorite ± albite ± muscovite ± quartz ± beryl assemblages typically extends to ca. 3 cm from the pegmatite/vein contacts; an intermediate zone containing biotite ± plagioclase + fluorite ± quartz assemblages extends to ca. 10 cm; and an outer sparse biotite ± quartz zone grades into unaltered amphibolite. The inner alteration zones experienced gains of H+, K+, F-, B3+, Be2+, Cs+, Rb+, Ta5+, Nb5+, As3+, y3+, and Sr2+; and losses of Si4+, Mg2+, Fe2+, Fe3+, Ca2+, Cr3+, V5+, and Sc3+; Cs+, Rb+, and As3+ have also migrated into the outer alteration zone. Oxygen isotope analyses of igneous and hydrothermal minerals indicate a single fluid (8180H2o' 8%0 of magmatic origin produced the pegmatite-vein system and hydrothermal alteration. The oxygen isotopic data, along with studies of the magmatic- hydrothermal transition in other miarolitic pegmatite districts, suggest that at Khaltaro emplacement of the pegmatite-vein system and associated amphibolite alteration and emerald mineralization occurred at temperatures between ..----.550 and 400°C, and at pressures ranging from 2 to 3 kbar. The unique occurrence of emeralds at Khaltaro results from introduction of Be2+, Si4+, A13+, K+, and Na+ in HF-rich fluids of magmatic origin, which caused hydrolysis of amphibolite and diffusion of released Cr3+ into the pegmatite-vein system. There, Cr3+ was preferentially incorporated into crystallizing beryl to cause emerald green coloration. Emerald Mineralization and Amphibolite Wall-Rock Alteration at the Khaltaro Pegmatite-Hydrothermal Vein System, Haramosh Mountains, Northern Pakistan by Brendan M. Laurs A THESIS submitted to Oregon State University in partial fulfillment of the requirements for the degree of Master of Science Completed January 17, 1995 Commencement June 1995 Master of Science thesis of Brendan M. Laurs presented on January 17, 1995 APPROVED: Redacted for Privacy Major Professor, representing Geology Redacted for Privacy Chair of Department of Geosciences Redacted for Privacy Dean of Gradu chool I understand that my thesis will become part of the permanent collection of Oregon State University libraries. My signature below authorizes release of my thesis to any reader upon request. Redacted for Privacy Brendan M. Laurs, Author Acknowledgments Drs. John H. Di lles, Lawrence W. Snee, and Ali H. Kazmi provided the inspiration for this project. In particular, Dr. Di lles supplied ever-helpful guidance and support throughout the course of this project, and Dr. Kazmi provided stimulating discussion and friendly accommodation in Karachi. The Geological Survey of Pakistan (GSP) provided logistical support in the field, sample preparation facilities, and XRF and XRD analyses; S. Hasan Gauhar and Allah B. Kausar coordinated logistics, and Yousef Warraich assisted with fieldwork. Dr. Nasir Ali Bhatti of the Gemstone Corporation of Pakistan (Peshawar) gave helpful advice and access to geologic reports. This study was funded by a Sigma Xi research grant, Chevron U.S.A. graduate fellowship (through Oregon State University (OSU) Department of Geosciences), National Science Foundation grant money (through Dr. Robert D. Lawrence), and the OSU Department of Geosciences Ore Deposit Research Foundation. Dr. Lawrence also provided a Khaltaro emerald sample for study, and access to his voluminous reference library. INAA analyses were made possible by the OSU Reactor Use Sharing Program (administered by Dr. Arthur G. Johnson); Martin Streck provided helpful advice, and Erwin Tome supervised sample preparation and data reduction. Dr. Roger Nielson provided instruction and advice for the electron microprobe; analyses were funded in part by the OSU College of Oceanic and Atmospheric Sciences. Dr. Reed Glasman supported XRD analyses and peak-search software at OSU Department of Geosciences, and Phong Nguyen performed computerized XRD mineral identification at OSU Department of Chemistry. David Maher carried out oxygen isotope analyses in the Dilles/Grunder lab at OSU Department of Geosciences, and Bill Rugh performed ICP-MS oxygen analyses at the OSU College of Oceanic and Atmospheric Sciences. Computer drafting of Figures 1 through 4 was performed by David Reinert. Table of Contents Introduction 1 Previous work 6 Sampling and analytical procedures 8 General geology 12 Petrology and geochemistry of host rocks 17 Garnet-mica schist 17 Amphibolite 19 Leucogranite 21 Pegmatites 26 Hydrothermal veins 28 Temporal and spatial relations of leucogranite, pegmatites, and veins 31 Emerald mineralization and beryl crystal chemistry 32 Petrology and geochemistry of amphibolite alteration 39 Biotite-tourmaline-fluorite zone 39 Biotite-plagioclase-fluorite zone 43 Sparse biotite zone 44 Whole-rock geochemistry of alteration 44 Oxygen isotopes 50 Discussion 53 Chemical exchange during amphibolite alteration 54 Relations between K- and Na-metasomatism 56 Be transport and emerald mineralization 57 Pressure and temperature conditions 58 Conclusions 60 Table of Contents References cited 61 Appendix 71 Table 1. Electron microprobe analyses of Khaltaro feldspar 72 Table 2. Electron microprobe analyses of Khaltaro garnet 83 Table 3. Electron microprobe analyses of Khaltaro amphibole 85 Table 4. Electron microprobe analyses of Khaltaro zoisite 91 Table 5. Whole-rock geochemistry of Khaltaro mica schist, amphibolite, and veins 94 Table 6. Electron microprobe analyses of Khaltaro biotite 100 Table 7. Electron microprobe analyses of Khaltaro muscovite 107 Table 8. Electron microprobe analyses of Khaltaro beryl 112 Table 9. Electron microprobe analyses of Khaltaro tourmaline 121 List of Figures 1.Regional geologic map of northern Pakistan 2 2.Geology and structure of the Khaltaro area 4 3. Map and cross section of Khaltaro Mine 1 area 15 4. Map of Khaltaro Mine 2 area 16 5.Chondrite-normalized trace element diagram of Khaltaro host rocks 18 6.Chondrite-normalized trace element diagram of Khaltaro leucogranites 24 7.Mineralogy and texture of pegmatite and veins at Khaltaro 27 8.Microprobe analyses from core to rim across a zoned beryl crystal 38 9.Representative diagram of half of a symmetrically zoned amphibolite selvage adjacent to a pegmatite or hydrothermal vein 38 10.Electron microprobe data of minerals occurring in leucogranite, pegmatite, veins, and amphibolite 42 11. Major element gains and losses in altered amphibolite 47 12.Trace element gains and losses within a single traverse of altered amphibolite 49 13.Schematic diagram showing exchange of components between pegmatites or hydrothermal veins and surrounding amphibolite, and conditions of emerald mineralization 53 List of Tables 1. Geochemistry of mica schist and amphibolite 9 2. Modal variation in unaltered amphibolite 20 3.Geochemistry of Khaltaro and Jutial leucogranites 23 4.Typical electron microprobe analyses of biotite and phlogopite from leucogranite, pegmatite, emerald, and altered amphibolite adjacent to vein 33 5.Typical electron microprobe analyses of muscovite from leucogranite, veins, and altered amphibolite adjacent to vein 34 6.Partial chemical analyses of beryl from pegmatite, veins, and altered amphibolite 36 7.Average microprobe analyses of tourmaline from pegmatite, vein, and altered amphibolite adjacent to vein 41 8.Geochemistry of altered amphibolite series adjacent to a tourmaline-albite vein 46 9.Oxygen isotope data of minerals from garnet-mica schist, amphibolite, leucogranite, pegmatite, and veins 51 Emerald Mineralization and Amphibolite Wall-Rock Alteration at the Khaltaro Pegmatite-Hydrothermal Vein System, Haramosh Mountains, Northern Pakistan. Introduction Emerald is a rare and valuable variety of beryl (Be3Al2Si6018) that derives its rich green color from trace amounts of Cr. Emeralds are rarely found in nature, because their formation requires the interaction of highly differentiated, Be-bearing granitic or pegmatitic fluids with mafic rocks containing Cr. Such exceptional geological conditions may take place in suture zones, granite/greenstone terranes, and metamorphosed shales (Kazmi and Snee, 1989). Suture-related