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Molybdenum Deposits BRITISH COLUMBIA DEPARTMENT OF MINES Hon. W. 1. ASSELSTINE, Mintster JOHN F. WALKER, Deputy Minister - BULLETINNo. 9 Molybdenum Deposits British Columbia bu JOHN S. STEVENSON 1940 . Key map showing principal molybdenite OCCwrenOeS in British Columbia. CONTENTS. Page 9 11 16 19 20 28 33 34 4.7 4.9 50 51 54 58 61 67 70 73 77 79 ILLUSTRATIONS. Page Keymap showing principal molybdenite occurrences in British Columbia ................................. Frontispiece Figure (1) - Anticlimaxmolybdenite property: pace, compass andbarometer survey ..................................... i!3 Figure (2) - Consolidated Miningand Smelting Company molybdeniteproperty, Boss Mountain.General plan of workings. Tape, compass survey........................................ :. _ ..................................................... 37 Figure (3) - ConsolidatedMining and Smelting Company molybdeniteproperty, Boss Mountain.Detail of creekshowings. Tape,compass survey ............................................................................................. 39 Figure (4) - Tidewater molybdenum property.Plan showing surfacegeology ..................................................................................... 61 Figure (5) - Tidewater molybdenum property.Plan show ing undergroundgeologyshowing I63 Figure (6) - Tidewater molybdenum property. Assay plan ................................................................................................................................................. ... I67 Figure (7) - Alliesmolybdenite property: pace, com- pass andbarometer survey ........................................................................... 76 Plate I, A - Mineralizedboulder on Stella molybden- iteproperty, showing typicalribbon- structure of vein, resulting from paper- thin layers of molybdenite in vein quartz. Boulder 3 feet long ...................................................... " ............................................ 12 Plate I, B - Twin peaks of Bossmountain .................................................................... 12 Plate 11, A - Camp of ConsolidatedMining and Smelting Company on their Bossmountain molybden- ite property; camp at headwaters of M olybdenite Creek Molybdenite 12 Plate 11, B - Specimenshowing brecciatednature of mineralizedfracture-zone, Bossmountain molybdeniteproperty of theConsolidated Mining and Smelting Company ................................................. 12 PREFACE. The presentbulletin includes geological descriptions of molybdenum deposits visited by the writer during the course of field work from 1937 to 1939, inclusive. ITith the excep- tion of the deposit at Alice Arm, all the more importantde- posits and many, thoughnot all, of theless important deposits inthe Province were visited by thewriter. J. T. Mandy of the Department of Minesexamined the Alice Arm deposit in 1939,and a synopsis of his report is included in this bulletin. To make the bulletin more comprehensive,an introductory chapter is included that briefly describes the mineralogy, geologicaloccurrence, metallurgy andeconomics of molybdenum An appendixhas been added to the bulletin in which brief notes are given concerning all the known occurrencesof molyb- denite in British Columbia that have come to the attention of the MinesDepartment. This appendix includes (1) occurrences fully described in this bulletin, marked with an asterisk, and (2) occurren'cesdescribed elsewhere as indicated by the key of references arid concerning many of whichonly incomplete in- formation is available. The writer wishes to acknowledge the kind assistance and cooperationrendered by mine officials and prospectors associ- atedwith the properties visited. Alan R. Smith,the writer's student assistant during the field seasons of 1938and 1939, greatly facilitated the field'work by his capable and hearty cooperation. INTRODUCTION. Molybdenum Minerals Thereare many molybdenum minerals,but only one, molyb- denite (MoS2) is of commercialimportance. The properties of molybdenite and of the more common molybdenum minerals are listed below. Molybdenite - Composition - Molybdenum sulphide, IwoS;! = molybdenum, 60.0 percent, sulphur, 40:O percent. Lustremetallic. Colour leadgray, bluish gray streak as com- paredwith the carbon-black streak of graphite. Opaque. Hard- ness, 1 to 1.5, Sectile. Laminae flexiblebut not elastic. Commonly foliated, in rosettes of crystals of finegranular. Molybdite - Composition - molybdenum trioxide, MoO3. Colour straw-yellow.Molybdite is oftenconfused with molybdic ocher. Common oxidation product of molybdenite. Molybdicocher - Composition - hydrous ferricmolybdate. Colouryellow. Often mistakenly called molybdite. Common oxi- dation product of molybdenite. Wulfehite - Composition - leadmolybdate, PbMoOq = molybdenum trioxide39.3 per cent, lead oxide, 60.7 percent. Lustre resinous - colourvaries, grey, brown, orange-yellow,olive- green,orange tobright red. Streak white. Subtransparent. Hardness 2-3. Fracturesubconchoidal. Occurs as tabular crys- tals or granular and massive. Powellite - Calciumjmolybdate,chillagite, lead molybdatewith leadtungstate, and koechlinite, bismuth molybdate, are rare. -1- GeologicalOccurrence The following notes concerning the geological occurrence of molybdenite are given to assist in evaluating types of molybdenite deposits that may be found during the course of prospecting for this mineral. Most molybdenite deposits are genetically related to ratheracid igneous rocks such as granite,granodiorite and quartz-diorite.Deposits associated with diorite and more basictypes are rare. 1n.most instances the deposit occurs w!!thin the body of the igneousrock itself, or close to it. Nolybdenitedeposits include the following types, listed inorder of importance:(1) silicified fracture-zones: (2) quartzveins; (3).pegmatites and aplites: (4) high-temper- aturereplacement deposits: (5j certaindisseminated chalcopy- rite deposits. Silicifiedfracture-zones are characterized by brecciated . rock, the fragments of whichhave been sealed by vein-quartz andmolybdenite. The molybdenite may occur as coarse plates along the fractures, or as very fine grains within the quartz veinlets. The form of ore-body is commonly that of a'pipe or stock with the vertical dimension greater than the horizontal. This type of deposit usuallypossesses a greater continuity of mineralization and resultant larger tonnage of ore than the other types of molybdenite deposits. Molybdenite-bearingquartz veins are widespread, but the amount of molybdeniteobtained from such deposits is not large. The veins range in width from a fraction of an inch to several feet, and fromshort lenses a few feet long to veinsseveral hundred feet in length. However, notonly are the veins often lenticular and discontinuousin length, but the molybdenite mineralization tends to be spotty in its distribution within the vein. For thesereasons it is alwayswise to do a consider- able amountof development on such a deposit before making com- mitments concerning possible tonnages. The mineralogy or" quartz-molybdeniteveins is simple,con- sisting usually of quartz,molybdenite and pyrite, and occasion- ally chalcopyrite, sphalerite and galena. Molybdenite-bearing pegmatite and aplite dykes are common, particularlyin eastern Canada. The form ora pegmatitedyke is apt to bedecidedly lenticular, aplites not so much so. The amount of molybdeniteobtained from pegmatites and aplites is notlarge, and, with a fewexceptions, most occurrencesare of more scientific than economicimportance. Two types of hightemperature replacement deposits cc-. casionallycontain a little molybdenite. One typecomprises bodies of lime-silicateand associated copper, iron and molyb- denum sulphides that have formed by replacement of limestone. Because of the common lenticular nature of limestonereplaoe- ment bodies and of the complex metallurgy necessary to extract themolybdenite from the intimately intergrown sulphides, that characterise this type of high temperature replacement deposit, thesedeposits are usually not of economic importance. The second type of high temperature replacement body is that where schists have been replaced by bodies that consist of quartz, feldspar,pyrrhotite andmolybdenite; they are probably close- lyrelated genetically to replacement-pegmatites. These re- placementbodies tend to be lenticular and sparselymineral.- ized by molybdenite. Most of thesedeposits are again of more scientificthan economicimportance, A type of deposit which is not represented in British Columbia andonly, so far as is known to the writer, found in thesouth-western United States andMexico, is that which con- sists largely of chalcopyrite and/or chalcocitedisseminated throughlarge bodies of graniticrocks, whichcontain a small amount of molybdeniteper ton. These deposits comprise large- scale coppermining operations and themolybdenite is recovered as a by-productmolybdenite concentrate from copper ores. Be- cause of thelarge tonnage of copperore treated, the amount of by-productmolybdenite is large. Such depositsinclude those at Bingham, Utah;Chino, New Mexico; Miami, Arizonaand Cananea,Mexico. Metallurgy Molybdeniteores always require concentration. It is not economically practical to hand-short mine-runore to a gradeacceptable by ferro-metallurgical plants, the ultimate purchasers of molybdenite. Inasmuch asthere are very few custom mills for molybdeniteores, and none in British Colum- bia, it is necessarythat any owner or prospectivepurchasw of a molybdenite property bear in mind the.probable necessity
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