Montana Tech Library Digital Commons @ Montana Tech Bachelors Theses and Reports, 1928 - 1970 Student Scholarship 4-1942 An Investigation of the Ores of the Big Seven Mine, Neihart, Montana Francis L. Wilson Follow this and additional works at: http://digitalcommons.mtech.edu/bach_theses Part of the Ceramic Materials Commons, Environmental Engineering Commons, Geology Commons, Geophysics and Seismology Commons, Metallurgy Commons, Other Engineering Commons, and the Other Materials Science and Engineering Commons Recommended Citation Wilson, Francis L., "An Investigation of the Ores of the Big Seven Mine, Neihart, Montana" (1942). Bachelors Theses and Reports, 1928 - 1970. 170. http://digitalcommons.mtech.edu/bach_theses/170 This Bachelors Thesis is brought to you for free and open access by the Student Scholarship at Digital Commons @ Montana Tech. It has been accepted for inclusion in Bachelors Theses and Reports, 1928 - 1970 by an authorized administrator of Digital Commons @ Montana Tech. For more information, please contact [email protected]. A N I_:'T V EST I GAT IOn Q..£ T:-1 E ORE S 0 r THE BIG S EVE H l.~ I N E, N E I II A n. T, 1~0 H T A !! A by Francis I.. Hilson A thesis submitted to the Departnent of Geology in pCtrtial fulf'illrJ.ent of rey_uirenents for the Degr-ee of Bachelor of Science in lleolo.3ical Engineering. ;,:ont.anaSchool of !,'ines '3utte, :~ontana April, 19/.v? IDNTAN,l. SCHOOL OF ~jNES lIBRARV. A ~ I N V' EST I GAT ION 0 F THE ORE S 0 F THE BIG S EVE N MIN E, NEIHART, MONTANA - by Francis L. Wilson n A thesis submitted to the Department of Geolo, in partial fulfillnent of requirements for the De ree of Bachelor of Science in Geolo ical Eneineering. ontan ,'3d~0C':;_ of Iti_1~s But t.e , ? ont an pril, 1942 TAB L E o F CONTENTS Results •••••••••••.••••••••••••••••••••.•••••••••••••••••••••••••••••• 1 Acknowl.edgemerrt s••••••••••••••••••••••••••••••••••••••••••••••••••••• 3 Introduction ••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 4 Source of Material •••••••••••••••••••••••••••••••••••••••••••••• 6 Laboratory Apparatus and Technique •••••••••••••••••• ·•••••••••••• 7 General Geology of the Neihart District ••••••••••••••••••••••••••••• ll Ore Depo sit s •••••••••••••••••••••••••••••••••••••••••••••••••••••••• 15 Tall Rock•••••••••••••••••••••••••••••••••••••••••••••••••••••• 15 Structurctl Feat.ur-es •••••••••••••••••••••••••••••••••••••••••••• 16 .iege.scopd,c Description ••••••••••••••••••••••••••••••••••••••••• 17 General Character of Super~ene Deposition ••••••••••••••••••••••••••• 19 llinerc. ..Lo gy •••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 23 Hypogene Ore l~inerals •••••••••••••••••••••••••••••••••••••••••• 23 Gangue }.{inerals •••••••••••••••••••••••••••••••••••••••••••••••• 26 Paragenesis ••••••••••••••••••••• o ••••••••••••••••••••••••••••••••••• 27 Conclusions ••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 30 Bibliography ••••••••••••••••••••••••••• ~•••••••••••••••••••••••••••• 32 LIS T o F ILLUSTRATIONS Plate I ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 23 II ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 24 III ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••.•• 26 Fig\l..i'e 1••••••••••••••••••••••••••••••••••••••••••••••••••••••• ••••• 18 2 •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 27 AN INVESTIGATION OF THE ORE S 0 F THE BIG S EVE N MIN E, N E I H ART, ION .T A N A by Francis L. Wilson RES U L T S During the course of this investioation of the ores of the Big Seven mine, Neihart, }.lontana,the writer has attempted, through a mi- croscopic study of polished sections, to ascertain the hypogene or su- pergene character of the ore minerals present in the ore suite. The samples, from ;hich the polished sections were made, were provided by the management of the Lexington lining Company from the Big Seven mine in Neihart, for 'Thoma copy of this manuscript 'will be prepared. A dis- cussion on the methods used in preparing polished sections, the reasons for drawing the conclusions herein presented, pictures of diagnostic evidence, seen in the polished sections, as \,[,ellas an account of the general geology of the Neihart district ill be found in the body of this paper. The folloTing is a summary of the author's res Its: HyPogene Ore Minerals Sphalerite Polybasite Galena pyrar ite Chalcopyrite Tetrahedrite Oxidized Ore inerals None observed. \ -1- Supergene Ore·Minerals None observed. Gangue liner~ls Pyrite Quartz Ankerite -2- ACKNOWLEDGEHENTS At the outset the author must gratefully acknowledge the 'Tilling cooperation of 1~. J. H. Cazier, manager of the Big Seven lline of the Lexington Hining Company, who went to such gr-eatlengths to collect and send the samples for this investigation. Sincere thanks must also be extended to Dr. Eugene S. Perry and Dr. George F. Seager of the Depart- ment of O-,eologyof Hontana School of Mines, who rer-e alrrays so ready to give any help or advice needed. Dr. Seager's Lectures and labora- tory lork on super ene enrichment and the microscopic recognition thereof proved of especial value. 11 data on the general geology of the Nei- hart district na s obtained from Paul J • Schafer's paper to whi.ch refer- ence i..-illbe made. 3imilarily, the data on supergene enrichment came from ~Tilliam H. Emmon's publications on sulfide enrichment, and also those of ~Ialdemar Lindgren. These books are listed in the bibliography as are those from whd.ch the aut or secured the information on the re- cognition of replacement structures. -3- I N T ROD U C T ION The compilor of statistics on mining companies, or even the close, yet non-technical observer of the mining industry, is probably awar-e of the large number of mines which st rt out in a vrild burst of activity, and then, within four to five years, close dO\ffiand nothing more is heard of them, except perhcps the dis runtled complaints of the stock- holders. It is an old story to the wining man. To begin lith, these mines or bonanzas, to use an old western term, are very promising; they pro- duce extremely rich ores ,hich require very simple metallurgical treat- ment; their ore bodies are fairly close to the surface, and seem to be quite extemsivd; the vein structures appear to continue in epth, and yet the mines close down , Vlhy? This is the natural reaction of our non-technical observer, and again it is the old story; the rich ores have suddenly become so Low grade that it is impossible to exploit them any further. nd so the eA~ensive surface plants ana equipment that '.lerepurchased and inst lled,cand the stock that was sold on the great expectations of the rich ore bodies, become worthless. There are concrete illustrations of the above statements, for ex- ample, several of the silver mines near Philipsburg, ontana, 'lhichare relatively snaLl.ow,have had to close dovm as their rich ores rere ex- hausted. In the Bannack-Argenta district in southwestern ont.ana, near- ly ever mine vcrked ceased operations at the extremely sha.Ll.o'f depth of 200 to 300 feet. nother example is in the eihart district itself, rher-e the .:ountainChief mine s 1ut dovm soon after a nev mill had been installed since the ore bec me too low _,radeto treat. On the other hand, there are many mines which st .rt out in much -h- .t.he same renner, and ore productive today at depth, from ores practi- c 1 '"(as rich as those near' the surface. This is exemplified by the copper mines at Butte, Montana. Here production started from workings above the 1000 foot level, and they are now producing from the 4100 foot level. There must be some explanation for some mines playing out at depth while others remain profitable as their development proceeds downwar-d, and the research work of the past two decades has bared the causes un- derlying the formation of these bonanzas. These causes and their re- sults have all been put forth under the principles of secondary or su- pergene enrichment. uany of short-lived bonanzas owe their character to the fact that their commercial deposits were rich supergene ores, formed in the shal- 101'. enriched zone by processes .to be explained later. 'lhereasthe pri- mary ores--the original ores deposited by ascending solutions from a magma reservoir--were poor in valuable minerals and needed the secondary processes to enhance the ore grade, so, '\'Thenthe secondary ores were exhausted, the mine necessarily had to close dovm. It seems hardly necessary to add that some mines start directly on the primary or hy- pogene ores and thus are able to follor.them in depth and still mine them pr-of'LtabIy , or, after exhausting their supergene ores, find their pri- mary ores also profitable, although perhaps not to the same degree. It is extremely pertinent, therefore, that all minino companies, especially those 'lorkingshallow deposits, should ascertain vhet.hertheir ore minerals are primary or secondary before investin in ex..ensive e- uipment. If they are pronounced econdcry , then the ore rna become ex- h,usted in a short time, nd it vould be a question as to the commercial possibilities of the undoubtedly lover grade primary ores. Therefore, . -5- the deposit should be mined more or less on a "shoest.r-Lng"until the primar ore is reached, and tenor determined. But if the ores are pri- mary, or if deeper primary ores are found to be commercial, extensive development and surface plants may be planned with more confidence. The properties of the Lexington Mining Company at Neihart,irom ~hich the ore samples investigated