Placer Examination - Principles and Practice
Technical Bulletin 4 Bureau of Land Management 1969
Table of Contents
1. GENERAL CONSIDERATIONS
An adequate mineral investigation will develop a considerable body of information in addition to that obtainable from samples alone, some of which will be found vital when assessing the actual worth of a prospect. For example: Sometimes most of the value in a commercial placer is found on or in the bedrock; perhaps several feet of bedrock must be taken up to recover the pay. In such cases its hardness and irregularities must be known and failure to consider this has proved fatal to more than one dredging project. Because boulders can be disastrous to a placer operation their maximum size, number, and distribution should always be of prime concern to the mineral examiner. Failure to recognize or properly assess tailings or muddy water disposal problems, where they exist, can prove expensive or cause premature shutdown of an otherwise profitable operation. In brief, physical details often determine the success or failure of a placer as much or more than the mineral content itself. The importance of considering all factors and their possible effect cannot be overemphasized.
Because no two deposits are alike, no rule can be made as to what should be included in a placer check list. Also, the degree of inquiry will vary widely depending on the purpose of the investigation. Where it is clearly evident that a property has no value or prospective value a detailed field investigation may not be required, but even here, sufficient data for a well-informed report should be gathered.
The following check list is intended first as a field guide and second, to show the range of inquiry which may be necessary for an adequate placer investigation. The user should, of course, tailor this list to suit his particular needs.
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