THE COPPER DEPOSITS OF MICHIGAN

By B. S. BUTLER and W. S. BURBANK

     Messrs. Broderick, Butler, and Hohl worked mainly on the general field problems, Professor Palache gave special attention to mineralogy, and Mr. Wandke worked partly in the field but gave special attention to the petrographic and mineralogic studies in the laboratory. Robert Hoffman spent the summer of 1920 and E. R. Lovell the summer of 1921 in the work. By a cooperative arrangement between Harvard University, the National Research Council, and the United States Geological Survey, R. C. Wells at the same time made a study of the chemistry of the formation of native copper. The chemists of the Calumet & Hecla Co. contributed analyses and other chemical data, especially in the early stages of the investigation. Augustus Locke was in frequent consultation with the other workers, and short periods were spent on the work by J. Volney Lewis, William Burns, and G. N. Bjorge. W. O. Hotchkiss and H. R. Aldrich, who have been working on the geology of the Keweenawan rocks for the Wisconsin Geological and Natural History Survey, visited the district and made interesting contributions to the discussion of the broader relations of the Keweenawan. Prof. A. C. Lane likewise gave the benefit of his long experience in the district.

     On the completion of the Calumet & Hecla investigation in the spring of 1924, an arrangement had been made by the United States Geological Survey after consultation with the other companies of the district, by which the general geologic results of the Calumet & Hecla study were turned over to the Geological Survey, which extended the study throughout the productive part of the district. Mr. Butler, reappointed on the Geological Survey, and W. S. Burbank were assigned to this work, which was carried on till August, 1925. A large part of this field work was done in association with the geological department of the Calumet & Hecla Co.

     During the last few years certain electrical methods of prospecting have been tried in the district with indifferent results, and in connection with this work Messrs. Broderick and Hohl started dip-needle surveys, which were successful in indicating the trend of different formations on the bedrock surface beneath the extensive covering of glacial drift. The results obtained were of such general interest that these gentlemen have kindly prepared a chapter on "geophysical methods applied to exploration and geologic mapping," which I has been incorporated in this report.

     Miss Marie J. Scholz compiled most of the statistical data for both the Calumet & Hecla Consolidated Copper Co. and the Geological. Survey and did most of the clerical work on the report. The drafting of the surface map and considerable of the other drafting was done by Carlos V. Rawlings.

      The general features of the geology and the occurrence of the copper and much of the detail for the north end of the district, as presented in this report, were mainly worked out during the Calumet & Hecla investigation by the men engaged in that work. The names of all these men appear in the title-page with the addition of W. S. Burbank. The report as it now stands was prepared by B. S. Butler and W. S. Burbank.

SCOPE OF REPORT

ACKNOWLEDGMENTS

     It is hardly necessary to say that any geologic report on an old district is likely to be but one of a series each based on the data accumulated by many others in addition to the authors, up to the time that it was made. This report is no exception to the rule and contains much information derived from earlier reports. The last general account of the region, however, was written about 15 years ago, and the mining developments - that have been carried on, at times very actively, during the period that has since elapsed have added greatly to the body of geologic fact that was then available.

     The main sources of information, apart from the work of the authors, have been the reports of the Michigan Geological Survey, previous reports by the United States Geological Survey, and the data accumulated by the operating companies. The Michigan Geological Survey generously furnished all material in its possession. All the mining companies of the district gave that hearty cooperation which was essential to the success of the report and without the assurance of which the survey would not have been undertaken. The help given by the different companies has, of course, not been equal. Those who had much gave much; some had little and could give no more than they had. The Calumet & Hecla Consolidated Copper Co. made the outstanding contribution, starting the work, and paying for a large part of it; and without this cooperation the report by the Geological Survey would not have been undertaken. Whatever of usefulness comes to the district from this report should be largely credited to that company.

     Acknowledgment to individuals who have published the results of their investigations is made under the heading "Previous investigations."  Acknowledgment to individuals for the data coming from companies is not easy, because information on any one topic has usually been accumulated over a long period and has been gathered by several individuals. The authors trust that they will be pardoned, therefore, if they do not try to accredit each borrowed fact to its original author but merge their acknowledgments of indebtedness in one expression of most cordial thanks to the officials of the companies. Several engineers of the district, especially Mr. R. R. Seeber and Mr. Herman Fesing, have furnished data for companies with which they were formerly connected but which at the time of the investigation were not operating. Mr. A. H. Meuche contributed many data on the south end of the district collected both while he was a member of the Michigan Geological Survey and later. Chemists of the Calumet & Hecla Co. have helped both by their interest and by analyses. For analyses the authors are indebted to Messrs. W. F. Hillenbrand and H. C. Kenney.

     In addition to the acknowledgments for contributions to the report, the authors wish to express appreciation for courtesies extended, especially by the Calumet & Hecla Co., to the Geological Survey and to them personally, which added much to the convenience and effectiveness of the work.

     To Mr. F. C. Calkins, of the Geological Survey, the authors are indebted for a critical reading of the report, which resulted in many helpful suggestions.

PREVIOUS INVESTIGATIONS

     Few other districts of the country have received such numerous and repeated examinations by geologists and engineers as have been made in the copper country of Michigan. Altogether a vast amount of information has been assembled regarding this district. Of that which has been published, most has been afforded by the State surveys of Michigan, Wisconsin, and Minnesota and by the United States Geological Survey. All known publications on the geology of the district are listed in the bibliography, but the contributions of several groups of workers are of so outstanding importance as to deserve special mention.