CONTENTS Melaphyre
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Department of the Interior Geography ............................................................................22 Roy O. West, Secretary Location .........................................................................22 Topography....................................................................22 Climate...........................................................................22 Industries .......................................................................22 U. S. GEOLOGICAL SURVEY Transportation................................................................22 George Otis Smith, Director Power.............................................................................23 Physiography ........................................................................23 Bedrock geology ...................................................................24 Professional Paper 144 Broader relations............................................................24 Location and extent....................................................24 Character of the rocks................................................24 THE COPPER DEPOSITS OF MICHIGAN Stratigraphy....................................................................25 Maps and sections .....................................................25 BY Age and relations .......................................................25 General character and distribution .............................25 B. S. BUTLER and W. S. BURBANK Sediments ..................................................................26 IN COLLABORATION WITH Distribution .............................................................26 General character ..................................................26 T. M. BRODERICK, L. C. GRATON, C. D. HOHL, CHARLES Conglomerate.........................................................26 PALACHE Felsite conglomerate ..........................................26 M. J. SCHOLZ, ALFRED WANDKE, and R. C. WELLS Extent and thickness of beds..........................26 Vertical distribution .........................................26 Character of material......................................26 Character of beds...........................................26 Character of underlying bed ...........................26 Source of material ..........................................27 Manner of deposition......................................27 Amygdaloidal conglomerate ...............................28 Relation to felsite conglomerate .....................28 UNITED STATES Origin..............................................................28 GOVERNMENT PRINTING OFFICE Sandstone and shale .............................................28 WASHINGTON Ash and tuff............................................................28 1929 Igneous rocks.............................................................28 Extrusive rocks.......................................................29 ADDITIONAL COPIES Distribution .........................................................29 OF THIS PUBLICATION MAY BE PROCURED FROM Extent of beds ....................................................29 THE SUPERINTENDENT OF DOCUMENTS Thickness ...........................................................29 U S GOVERNMENT PRINTING OFFICE Composition of flows ..........................................30 WASHINGTON, D. C. AT Textural types.....................................................31 $2.50 PER COPY Ophite.............................................................31 Porphyrites .....................................................31 Glomeroporphyrites........................................31 CONTENTS Melaphyre.......................................................31 Dolerite...........................................................31 Outline of report.......................................................................... 2 Relation of texture to composition ......................31 Distribution of the different rocks ........................32 Geology.................................................................................. 2 Character of eruptive rocks ................................32 General features...............................................................2 Location of volcanic vents ..................................33 Lava tops or amygdaloids.................................................3 Amygdaloids ..........................................................33 Oxidation of lavas.............................................................3 Trap....................................................................33 Copper in trap...................................................................3 Bottom amygdaloid layer....................................34 Structure...........................................................................3 The lava tops......................................................35 Ore deposits ........................................................................... 3 Varieties .........................................................35 Conglomerate lodes .........................................................4 Smooth tops ...................................................35 Amygdaloid lodes .............................................................4 Fragmental or brecciated tops........................36 Ore shoots........................................................................4 Character....................................................36 Mineralized fissures..........................................................4 Origin..........................................................38 Changes with depth..........................................................4 “Scoriaceous tops” .........................................40 Genesis of the deposits....................................................4 Alteration................................................................41 Part 1. General features ............................................................ 5 Alteration of traps ...............................................41 Alteration of the lava tops...................................41 Introduction............................................................................. 5 Red color of amygdaloid tops .............................41 Field work and authorship ................................................5 Statement of the problem ...............................41 Scope of report.................................................................6 Red tops of unaltered western flows ..............42 Acknowledgments ............................................................6 Oxidation in smooth-top flows of Keweenawan Previous investigations.....................................................6 series..................................................................42 Bibliography......................................................................7 USGS Professional Paper 144 – The Copper Deposits of Michigan – Part 1 – Page 1 of 69 Oxidation and concentration in brecciated-top 65. Alteration and replacement of minerals...........................60 flows ...................................................................43 Mineralogic features ...........................................46 66. A, Porcelanic datolite inclosing copper; B, Mammillary Cause of iron oxidation and concentration..........47 surface of porcelanic datolite..........................................60 Modern weathering.........................................47 67. A, Intergrowth of copper and silver; B, Fissure breccia Independent solutions.....................................47 partly replaced by datolite; C, Native silver on native Surface weathering immediately after copper. ...........................................................................60 extrusion .........................................................48 Hydrothermal alteration ..................................49 68. Relation of sulphides and other minerals. .......................60 Atmospheric oxidation of hot tops...................50 FIGURE 1. Variation in thickness of Kearsarge flow ...............29 Magmatic processes.......................................50 Magmatic segregation ................................50 2. Change in iron in lava top at Twin Falls, Idaho..................42 Fumarolic alteration ....................................51 3. Iron content of smooth-top flow.........................................43 Action of gases from the flows....................51 Copper content of the basalts.................................53 4. Iron content of Kearsarge flow. .........................................43 Intrusive rocks ........................................................55 General features.................................................55 5. Gains and losses in constituents in oxidized tops, as Quartz porphyry and felsite.................................55 compared with trap portions of flows..............................49 Basic dikes .........................................................55 6. Change in character and content of iron in different parts of Age of intrusive rocks .........................................55 lava flows. ......................................................................50 Structure.........................................................................56 Folds ..........................................................................56 7. Stability relation for the equation Fe3O4 + CO ⇄ 2FeO + Faults..........................................................................56