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Placer Examination Principles and Practice

Bureau of Land Management

Technical Bulletin 4

This bulletin has been the defacto standard for Placer Mining since it was first published. It provides a complete picture of how to define a placer, measure its reserves, Sample correctly, Assay, and how to develop the placer into production.

• PREFACE
• PART I - REVIEW OF PLACER THEORY AND GEOLOGY

• 1. Placers Defined
• 2. Study of Placers — General
• 3. Sources of Valuable Mineral
• a) Lodes or mineralized zones
• b) Erosion of pre-existing placer deposits
• c) Low-grade auriferous conglomerates or glacial debris
• d) Magmatic segregations and associated basic rocks
• e) Regional rocks containing particles of valuable mineral
• 4. Weathering and Release Processes
• a) Ground water
• b) Temperature change
• c) Plant growth
• d) Surface erosion
• 5. Stream Processes Related to Placers
• 6. Concentration of Valuable Minerals
• a) Bedrock concentrations
• b) Types of bedrock
• c) Pay streaks
• 7. Preservation of the Deposit
• a) Abandonment
• b) Regional uplift
• c) Burial
• PART II - TYPES OF PLACERS

• 1. Residual Placers
• 2. Eluvial Placers
• 3. Stream Placers
• a) Gulch placers
• b) Creek placers
• c) River deposits
• d) Gravel plain deposits
• 4. Bench Placers
• 5. Flood Gold Deposits
• 6. Desert Placers
• 7. Tertiary Gravels
• 8. Miscellaneous Types
• a) Beach placers
• b) Glacial deposits
• c) Eolian placers

• PART III - SAMPLING AND EVALUATION

• 1. General Considerations
• a) Problems
• b) Industry practice
• c) Minerals other than gold
• d) Other factors to be considered
• e) In brief
• 2. Sampling Guides
• a) Reconnaissance
• b) Choosing a sampling method
• c) Number and size of samples
• 3. Sampling Methods
• a) Existing exposures
• b) Hand-dug excavations
• c) Machine-dug shafts
• d) Backhoe excavators
• e) Bulldozer trenches
• f) Sampling with churn drills
• g) Bulk samples
• h) Grab samples
• i) Drift mine sampling
• j) Hydraulic mine sampling
• 4. Special Problems
• a) Large rock or boulders
• b) Erratic high values
• 5. Uncased or Small-diameter Drill Holes
• 6. Salting
• 7. When Sampling Fails
• PART IV - SAMPLE WASHING EQUIPMENT
• 1. General Considerations
• 2. Miner's Pan
• 3. Sluice Box
• 4. Rockers
• 5. Special Machines
• 6. Dry Washers
• PART V - PANNING AND ASSAY PROCEDURES
• 1. Panning
• 2. General Notes on Panning with Suggestions
• For Improving Procedure
• 3. Fire Assay of Placer Samples — Misleading Results
• 4. Procedure For Determining Recoverable Gold in Placer Samples
• PART VI - NOTES ON GENERAL PRACTICE
• 1. Description of Samples
• 2. Reduction of Sample Volumes
• 3. Reporting Values
• 4. Cost Estimates
• 5. New or Unproven Processes
• PART VII - CHECK LIST FOR PLACER INVESTIGATIONS
• 1. General Considerations
• 2. Field Guide and Check List (example)
• PART VIII - GLOSSARY OF PLACERS TERMS
• APPENDIX
• A. Placer Sampling Forms
• B. Gold Price and Value Data
• C. Water Data
• D. Placer Drilling Data
• E. General Information and Cost Data
• F. Conversion Tables

* This document was digitally archived by Sylvanite, Inc. and is not to be used for resale or reproduction. You are not purchasing the original document but a PDF version that will be emailed to you with a downloadable link for your item.