Mineralogical, Textural, and Metal Residence Studies of Primary, Recrystallized, and Remobilized Ores of the Greens Creek Deposit By Cliff D. Taylor, Steven J. Sutley, and Frederick E. Lichte Chapter 9 of Geology, Geochemistry, and Genesis of the Greens Creek Massive Sulfide Deposit, Admiralty Island, Southeastern Alaska Edited by Cliff D. Taylor and Craig A. Johnson Professional Paper 1763 U.S. Department of the Interior U.S. Geological Survey Contents Abstract .......................................................................................................................................................187 Introduction.................................................................................................................................................187 Mine Location, General Host Rocks, Metamorphic History, Deposit Morphology, and Structural History .................................................................................................................189 Previous Mineralogical and Mineral Geochemical Studies ...............................................................191 Ore Types .....................................................................................................................................................194 Primary Ore Mineralogy and Textures ...................................................................................................196 Recrystallized and Remobilized Ore Mineralogy and Textures ..........................................................196 Free Gold—Mineralogy and Textures ....................................................................................................199 Paragenetic Relationships—Physical and Chemical Modification of Ores ....................................200 LA–ICP–MS Mineral Chemistry Studies ................................................................................................204 Methods..............................................................................................................................................204 Results ................................................................................................................................................209 Discussion ...................................................................................................................................................230 Conclusions.................................................................................................................................................234 References Cited........................................................................................................................................234 Figures 1. Maps of northern Admiralty Island showing the location of the Greens Creek mine and other features mentioned in the text. ...................................................................191 2. Plan and cross-sectional views of the Greens Creek deposit showing features described in the text. ................................................................................................................192 3. Photographs of hand samples illustrating the various massive sulfide and white ore types .....................................................................................................................................194 4. Photographs of hand samples illustrating textures present in various ore types .........197 5. Photomicrographs of polished thin sections showing primary mineral textures ..........198 6. Photomicrographs of polished thin sections showing recrystallized ore textures .......201 7. Photomicrographs of arsenian pyrite and arsenopyrite in polished thin sections .......205 8. Photographs and photomicrographs of free gold (Au) in hand samples and polished sections ......................................................................................................................207 9. LA–ICP–MS traverses across heavy concentrate grains recovered from the Greens Creek mill ......................................................................................................................208 10. Photographs and photomicrographs showing textural relationships in Greens Creek ores ..................................................................................................................................210 11. Summary LA–ICP–MS data on sulfide ore minerals in the Greens Creek deposit. Box plots of percentiles shows the log10 concentration range for primary, recrystallized, and remobilized ore textures for each of 19 elements .............................212 12. Single element plots of LA–ICP–MS data showing the range of elemental abundances of metals in primary and recrystallized pyrite and sphalerite, and in primary, recrystallized, and remobilized galena ......................................................221 Tables 1. Greens Creek ore mineralogy—minerals identified ...........................................................188 2. Trace-element composition of primary pyrite as determined by Laser Ablation–Inductively Coupled Plasma––Mass Spectroscopy analyses .........................213 3. Trace-element composition of recrystallized pyrite as determined by Laser Ablation–Inductively Coupled Plasma––Mass Spectroscopy analyses .........................214 4. Trace-element composition of arsenian pyrite as determined by Laser Ablation–Inductively Coupled Plasma––Mass Spectroscopy analyses .........................215 5. Trace-element composition of galena as determined by Laser Ablation–Inductively Coupled Plasma––Mass Spectroscopy analyses .........................215 6. Trace-element composition of sphalerite as determined by Laser Ablation–Inductively Coupled Plasma––Mass Spectroscopy analyses .........................216 7. Trace-element composition of tetrahedrite as determined by Laser Ablation–Inductively Coupled Plasma––Mass Spectroscopy analyses .........................217 8. Trace-element composition of mixed primary-textured mineral aggregates as determined by Laser Ablation–Inductively Coupled Plasma—Mass Spectroscopy analyses ...........................................................................................................218 9. Trace-element composition of recrystallized mixed mineral aggregates as determined by Laser Ablation–Inductively Coupled Plasma––Mass Spectroscopy analyses ...........................................................................................................219 10. Trace-element composition of remobilized mixed mineral aggregates as determined by Laser Ablation–Inductively Coupled Plasma––Mass Spectroscopy analyses ...........................................................................................................220 Mineralogical, Textural, and Metal Residence Studies of Primary, Recrystallized, and Remobilized Ores of the Greens Creek Deposit By Cliff D. Taylor, Steven J. Sutley, and Frederick E. Lichte Abstract of massive sulfide mineralization at Greens Creek occurred primarily during early diagenesis, synchronous with accumu- The Greens Creek deposit is a 24.2-million-ton poly- lation of the hanging-wall sediments. The early development metallic massive sulfide with a diverse base- and precious- of framboid-derived, atoll-shaped textures in the ores may metal-rich mineralogy, which has been subjected to regional indicate that a zone-refinement process occurred in the pres- lower greenschist facies metamorphism. Roughly 30 percent ence of colloidal base-metal-sulfide gels. Metamorphic recrys- of the ores retain primary mineralogy and mineral textures tallization produced advanced atoll-shaped structures in the as well as gross original ore stratigraphy. Ore lithologies fall ores and resulted in much coarser textures and the formation into two groups: massive sulfide ores (greater than 50 percent and(or) remobilization of secondary, precious-metal-enriched sulfides) and semimassive or disseminated sulfide gangue-rich minerals. Secondary minerals are present as matrix to pyrite “white” ores (less than 50 percent sulfides). There are two euhedra and in late fractures and veinlets. Secondary mineral- types of massive ore: massive pyritic and massive base-metal- ogy includes chalcopyrite, sphalerite (low iron), galena, free rich ore. The white ores are of three types: white carbonate gold, electrum, tetrahedrite (antimony-rich), pyrargyrite, and and white siliceous ores (common), and white baritic ore. All many other sulfosalt minerals. Metamorphism resulted in vis- the ore types can be further subdivided on the basis of modi- ible cleaning and coarsening of the ore mineralogy and caused fication by veins, breccias, and gouge or rubble zones pro- local trace-element redistribution and upgrading of the ores. duced during faulting or folding. Veining due to metamorphic remobilization and recrystallization can result in enrichment of free gold and a variety of silver-sulfosalt minerals. The ore Introduction stratigraphy at Greens Creek is characterized by proximal copper-arsenic-gold-enriched massive pyritic ores centered The Greens Creek deposit is a mineralogically diverse, over white siliceous ores and silicified footwall. Laterally, the polymetallic (zinc-lead-silver-gold-copper) massive sulfide of white siliceous ores grade outward into white carbonate and Late Triassic age and unusually high silver content. The global barite ores. White ores are overlain by massive pyritic ores that resource is currently 24.2 million tons at an average grade of change upward