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Geology of the Bohemia Mining District, Lane County, Oregon

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Geology of the Bohemia mining district, Lane County, Oregon Item Type text; Dissertation-Reproduction (electronic) Authors Lutton, R. J. Publisher The University of Arizona. Rights Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author. Download date 03/10/2021 21:47:27 Link to Item http://hdl.handle.net/10150/565597 GEOLOGY OF THE BOHEMIA MINING DISTRICT, LANE COUNTY, OREGON . :■ . ■: -■ by .. : U".: J Richard JC. Lutton * - -r" - A Thesis Submitted to the Faculty of the DEPARTMENT OF GEOLOGY In Partial Fulfillment of the Requirements For the Degree of DOCTOR OF PHILOSOPHY In the Graduate College THE UNIVERSITY OF ARIZONA c: 1962 THE UNIVERSITY OF ARIZONA GRADUATE COLLEGE I hereby recommend that this dissertation prepared under my direction by Richard J. Lutton entitled "Geology of the Bohemia Mining District, Lane County, Oregon" be accepted as fulfilling the disserta­ tion requirement of the degree of Doctor of Philosophy. jr . Dissertation Director Efcte After inspection of the dissertation, the following members of the Final Examination Committee concur in its approval and recommend its acceptance:* 9. /% % ^ J 9 & ^ /fto ♦This approval and acceptance is contingent on the candidate's adequate performance and defense of this dissertation at the final oral examina­ tion. The inclusion of this sheet bound into the library copy of the dis­ sertation is evidence of satisfactory performance at the final examina­ tion. STATEMENT BY AUTHOR : ■ / ' v- . y-j :;. :..a ■■ rvr.;.: AA'nAC'A This thesis has been submitted in partial fulfillment of require­ ments for an advanced degree at The University of Arizona and is de­ posited in The University Library to be made available to borrowers under rules of the Library. Brief quotations from this thesis are allowable without special permission, provided that accurate acknowledgment of source is made. Requests for permission for extended quotation from or reproduction of this manuscript in whole or in part may be granted by the head of the major department or the Dean of the Graduate College when in their judgment the proposed use of the material is in the interests of scholar­ ship. In all other instances, however, permission must be obtained from the author. A':, x : SIGNED: : : - ' x ;r; X, (i": C ; X; :■ v;ro ' : o.:x A. /.-X ; / ' 1 / x: XV' I;XVx; XX"' : r L..: :X ' ; xx ' ' /A ; ' . V - i - 1 ’ ' X • , ■ ^ | 1 - - A XL ■: '1 X. •- 1 ’ LX I x X, - v. ; \ , : - GEOLOGY OF THE BOHEMIA MINING DISTRICT, LANE COUNTY, OREGON . ] ' . ■ by . \ : ... ■ : ■: - - ; ; ;iin Richard J. Lutton , ABSTRACT -y : • v.r - : ' ; y ' : y.v. ? 1 y r n .. '.H The base- and precious-metal quartz veins of the Bohemia ,v '':: . : v-: . r 'y' ' ; y;: . /’ y mining district are genetically related to middle Tertiary granitoid in- trusives of the same igneous cycle that formed the volcanic country : : " i y ,:i:v ■ C-. vy in . ;.r i'.y n;'; '- : W >■ ' rock. About two thirds of the volcanics c lo s e d in the immediate area are pyroclastics, mostly lapilli tuff that was deposited in a fluvial y;>yy y : ' y y ■ y : y ': ' ‘y : . o \yyy y. y :-.y - 1: y : 'O .: -y y:; ':; ,; : ; v environment. The remainder are mostly flows of basalt, andesite, ry..i ' - :-y' ::y. •: ' ' y . y - y y ; y y ; .::y . y • >y ' y y ' • dacite, and rhyolite. Local centers fed the flows through hypabyssal • - yy’ 'y yyyyy dikes and plugs and viscous domes. The basement structural grain has probably determined the pattern of early intrusives. f.-oyy L ' y y: / ;r ; • ' ' ' y- y y." :r - y ;y : '= yy: : .:" A composite stock of granodiorite and quartz diorite has been intruded along a north-northeast line parallel to the axis of the Western y .' :-y y y .-y. ;yy.v. y-^y :;i y y yy; yV - ;yy.,y Cascades province. A large percentage of the rocks of the area are propylitized, and in a wide aureole of contact alteration surrounding the stock, the pyrbclastics have at least locally been metamorphosed to the albite-epidote hornfels facies. Somewhat later metasomatism has re­ placed country rock and the intrusives with quartz, sericite, and tour­ maline along restricted zones*:: i- i U i . i : t * The granitoid intrusives warped the gently dipping volcanics and developed a system of longitudinal arid.transverse fractures. Dis­ tention of the fracture system by the intrusives and subsequent normal faulting on individual fractures during the period of mineralization has provided space for deposition of vein minerals. Epidote, specularite, chlorite, and quartz locally accompany minor sphalerite, chalcopyrite, galena, and pyrite in an early stage of vein filling. During intermediate stages, the silica, with or without contemporaneous hematite and sul­ fides, accumulated in horizontal layers under the influence of gravity. Such bedding suggests a low specific volume for the hydrothermal fluid, and therefore, it also suggests a moderate temperature at the prevail­ ing shallow depth. Mechanical washing of siliceous and minor argillaceous debris from the oxidized zone to just below the water table in the vein has de­ veloped secondary vein sediments. Secondary wad, which is inter- bedded with clastic debris in the oxidized zone, probably results from hydrolysis of manganese dissolved from carbonate gangue. iii The relatively low economic potential of the Cascades metal- logenetic province is considered to be a consequence of the position near the edge of the continent and of the old age of mineralization with respect to the beginning of andesitic volcanism. Ore controls in the Bohemia district include: 1) proximity to the center of mineralization, which was probably a cupola; 2) open channels, which resulted from preferential dilation of steep segments of irregular veins; 3) a concentration of subsidiary veinlets; and 4) vein intersections. • ‘ ’ 1 f ' '■ ( , ' iv TABLE OF CONTENTS Page INTRODUCTION ..... ------------- ------------------------------------- 1 Previous Work . 1.............................................................................. 2 Procedure of Investigation .'............................................................ 3 Acknowledgments .......'.....:................................................... 4 VOLCANIC AND SEDIMENTARY ROCKS............... ............................. 6 Lower Unit 7 Massive Pyroclastics 7 Tuffaceous Shale and Sandstone . 1 . 8 -J ) Intermediate U nit. i 8 •:?. D om es................................................................................ 9 ^ :- Flows ................................................................................ 12 Pyroclastics............... .................................................... 13 Petrography of the Lavas of the Intermediate. Unit 15 Upper U nit................................................................................ 17 Basic Lava................................ .................................................... 17 'Vi­ Bohemia Mountain F lo w s............................................... la Grouse Mountain F lo w s ........................... .................... 19 Basalt of North Fair view Mountain ............................ 19 ' Porphyritic Basalt of Champion Creek .............. ........ 19 Porphyritic Basalt of Annie Creek.............................. 20 -x ' V: ■ i. : ....................... v v Intercalated Pyroclastics .......................... .. 20 Dacites and R hyolite................................................................ 21 r; ; -- i ‘Dacite of Grrouse ^4ountam.. ... ............. , 21 Rhyolite East of Noonday Ridge ......... ................... 21 v Page . : : Petrography of the Basic Flows of the Upper Unit...... 22 INTRUSIVE ROCKS .................................................................................. 27 Porphyritic Dacite .......................................... 27 Basic Hypabyssal Rocks .................. 28 r1 ... .. : .. : , , . • ................................... * , ^ . ; > J Glen wood S i l l ............................................ 29 Basalt Near Elephant Mountain.......... 30 Porphyritic Basalt Near Musick Mine. 30 Bohemia Stock and Associated Bodies.... ... 31 Augite Diorite ..; ................................................. 33 Porphyritic Augite-Quartz Diorite ............ 34 Dacite Porphyry ..................................................... 35 Quartz Phenocryst-B earing Dacite Porphyry . 36 Granodiorite and Porphyritic Granodiorite .... 37 Coarse Inclusions in Porphyritic Granodiorite 40 Granite Porphyry .............................................. .... 41 ' Xi ...... .. STRUCTURE ............................................................................ 42 Homocline ___________ __..........___...... 42 Broad Warp ........................................................... 42 Minor Folds .........:.. r........... ..... 43 Veins and F a u lts................................................... 43 Joints ......................;............ 45 Basement Structure ....................... '47 GV ALTERATION 49 C arbonatization 50 Calcite Associated With Hypabyssal Rocks 50 Pervasive Carbonatization ............................ 51 .H Contact Alteration .. 51 Biotitization........... 54 Tourmalinizatibn ... 54 Sericitization ..... 57 Page Argillization...................................................................................... 58 Pyritization........................................................................................
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