Assay Data

    in Geology

    Records of the results of sampling form a highly important part of the geologist's basic data. Assay results may be shown on the geologic maps themselves, but it is usually preferable to present them on a sep¬arate set of plans and sections. These should be drawn on sheets of tracing cloth with margins corresponding exactly to the geologic maps so that the one may be superimposed on the other.

    Since numeráis take up considerable space the individual assays can be shown only on the maps of large scales. For scales of 100 feet to the inch or smaller it will be necessary to present assay data either in the form of averages or by some graphic method (see p. 193).

    Kecording Samples. In recording assay data the object is not merely to get the information written down but to present it in form that can be sized up without loss of effort. Toward the preparation of neat and convenient maps, the following rules are helpful. Although some of them may seem obvious, I have seen all of them violated, often with confusing results.

    1.      Omit sample numbers from the map. They take up space and serve no useful purpose once the location of the sample is fixed.

    2.      Enter the sample results close to the place in which the sample was cut. A map with "skyrockets" pointing in all directions to tables of results is not a sample map but merely a keyed list, and usually merits a less dignified description.

    3.      Tabulate the sample data in columns or rows with the same data in each column or row in order that the figures may be scanned rapidly.    Do not make the eye skip figures.

    4.      Record the content in each metal separately. Do not add up the value and merely record the total in dollars.

    5.      Record gold values in grams, in ounces, or, if local custom decrees, in pennyweights; use units and decimals. (Nothing is more awkward than the outmoded custom of recording ounces, pennyweights, and grains.)  State on the map what the unit is. Don't record gold values in dollars or in shillings but if you do disregard this rule, state on the map what price is used in arriving at the value.

    6.     If dollars are used, the second decimal is not significant except in placer deposits and should be dropped to save space.  If hundredths of feet are obtained as a result of converting inches to decimals, the second decimal is like-wise not a significant figure.

    In recording samples the values should be placed on the map as re-ported by the assayer; high values should not be reduced unless they are out-and-out mistakes, for they may be of geological significance even though they are not entitled to full weight in calculation.