SPECIAL PUBLICATION 87 PLACERPLACER GOLDGOLD RECOVERYRECOVERY METHODSMETHODS By Michael Silva 1986 CALIFORNIA DEPARTMENT OF CONSERVATION DIVISION OF MINES AND GEOLOGY GORDON K. VAN VLECK, Secretary GEORGE DEUKMEJIAN, Governor DON L. BLUBAUGH, Director THE RESOURCES AGENCY STATE OF CALIFORNIA DEPARTMENT OF CONSERVATION DIVISION OF MINES AND GEOLOGY JAMES F. DAVIS STATE GEOLOGIST SPECIAL PUBLICATION 87 PLACER GOLD RECOVERY METHODS By Michael Silva 1986 CALIFORNIA DEPARTMENT OF CONSERVATION DIVISION OF MINES AND GEOLOGY 801 K Street Sacramento, California 95814 CONTENTS INTRODUCTION ............................................................................................................................................... 1 CONCENTRATION OF PLACER GOLD ORE .................................................................................................. 2 SMALL SCALE RECOVERY EQUIPMENT ....................................................................................................... 2 Gold Pan.................................................................................................................................................. 2 Rocker ..................................................................................................................................................... 3 Construction ...................................................................................................................................... 3 Assembly........................................................................................................................................... 5 Operation .......................................................................................................................................... 5 Sluices ..................................................................................................................................................... 6 Long Tom .......................................................................................................................................... 7 Dip-Box ............................................................................................................................................. 8 Shaking Tables ........................................................................................................................................ 8 Portable Processing Equipment ............................................................................................................ 10 Amalgamation........................................................................................................................................ 10 DRY PLACERS ............................................................................................................................................... 10 Dry Washers .......................................................................................................................................... 10 Air Tables (Oliver Gravity Separator) ..................................................................................................... 11 MODERN RECOVERY EQUIPMENT ............................................................................................................. 12 Pinched Sluice Systems ........................................................................................................................ 12 Spiral Concentrators .............................................................................................................................. 13 Rotating Spirals ............................................................................................................................... 15 Helixes ............................................................................................................................................ 15 Jigs ........................................................................................................................................................ 16 Fine Material Separators ....................................................................................................................... 20 Bartles-Mozely Separator ................................................................................................................ 20 Bartles CrossBelt Separator ............................................................................................................ 21 Centrifugal Concentrators ...................................................................................................................... 21 Bowls............................................................................................................................................... 21 Knelson Concentrator ..................................................................................................................... 22 SUMMARY ...................................................................................................................................................... 22 OPERATING MINES ....................................................................................................................................... 23 Hammonton Dredge .............................................................................................................................. 23 Hansen Brothers - Hugh Fisher ............................................................................................................. 25 Bear River ....................................................................................................................................... 26 Greenhorn Creek ............................................................................................................................ 26 TRI-R Engineering - Stinson Mine ......................................................................................................... 27 SELECTED ANNOTATED REFERENCES ...................................................................................................... 29 APPENDIX: LIST OF EQUIPMENT MANUFACTURERS AND SUPPLIERS .................................................. 31 TABLE Table 1. Range of particle sizes effectively treated by various types of separation equipment ....................... 23 DISCLAIMER COMPANY NAMES AND PRODUCTS DESCRIBED IN THIS PUBLICATION ARE FOR DESCRIPTIVE PURPOSES ONLY AND DO NOT IMPLY ENDORSEMENT BY THE STATE OF CALIFORNIA, DE- PARTMENT OF CONSERVATION, DIVISION OF MINES AND GEOLOGY. CONVERSELY, THE OMIS- SION OF A COMPANY OR PRODUCT DOES NOT IMPLY REJECTION BY THE DEPARTMENT OF CONSERVATION, DIVISION OF MINES AND GEOLOGY. ILLUSTRATIONS Figures Figure 1. Rocker washer ............................................................................................................................................................... 3 Figure 2. Rocker parts and construction ....................................................................................................................................... 4 Figure 3. Classifying action of sluice riffles ................................................................................................................................... 6 Figure 4. Hungarian riffle arrangement ......................................................................................................................................... 6 Figure 5. Detail of Hungarian riffles ............................................................................................................................................... 7 Figure 6. Side and plan views of a long tom ................................................................................................................................ 7 Figure 7. Shaking table concentrator ............................................................................................................................................ 8 Figure 8. Mineral separation on a shaking table ........................................................................................................................... 9 Figure 9. Stratification of minerals along shaking table riffles ....................................................................................................... 9 Figure 10. Denver Gold Saver ...................................................................................................................................................... 9 Figure 11. Dry washer ................................................................................................................................................................. 11 Figure 12. Separation on an air table or pneumatic shaking table .............................................................................................. 11 Figure 13. Oliver gravity separator .............................................................................................................................................. 12 Figure 14. Mineral separation on an Oliver gravity separator ..................................................................................................... 12 Figure 15. Cross section and plan view of pinched sluice .......................................................................................................... 12 Figure 16. Schematic diagram of a single Reichert cone ........................................................................................................... 13 Figure 17. Humphries spiral concentrator ..................................................................................................................................