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Nephrite in British Columbia

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Nephrite in British Columbia NEPHRITE IN BRITISH COLUMBIA, by JOHN ROSS FRASER B.Sc, University of British Columbia, 1967 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in the Department of Geology We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA December, 1972 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of The University of British Columbia Vancouver 8, Canada Date v^a^-.5.a.1 \<2>7 3 (i) ABSTRACT Nephrite is a compact, microfibrous variety of actinolite-treraolite in which bundles or tufts of minute fibers of the amphibole are twisted and thoroughly felted or interwoven with one another, producing a characteristic "nephritic" microstructure. In British Columbia, nephrite deposits, both in place and placer, are closely associated with a belt of alpine ultramafic rocks that extends for 1000 miles from the Hope area, east of Vancouver, northwestward to the Yukon border. The three major nephrite producing regions are the Bridge River - lower Fraser River area, the Takla Lake area and the Dease Lake area. The nephrite from British Columbia contains, in addition to essential tremolite, small amounts of chlorite, uvarovite, chrome spinel, diopside, talc, carbonate, sphene, phlogopite and pyrite. Grains of chrome spinel and uvarovite are usually visible in hand specimen. The colour of the majority of the specimens is yellowish green; this colouration is caused by the presence of iron in both the divalent and trivalent states. Polished surfaces of the 2 nephrite have an average Vickers hardness of 950 Kg/mm and an average Mohs hardness of 7. The average specific gravity is 3.00. The unit cell parameters of tremolite from British Columbia nephrite specimens are similar to those of nephritic tremolite from Siberia. X-ray diffraction data for the tremolite from these specimens are also in good agree- (ii) merit with those for nephritic tremolite from other localities. The nephrite specimens contain an average of 3.05 percent iron; small amounts of cobalt, nickel, manganese, copper, lead, zinc, chromium, titanium and vanadium are also present. Significant regional variations in the averages for iron, cobalt, manganese, copper, lead, zinc and vanadium are not observed when the specimens are grouped according to the area of origin; slight varia• tions are observed in the average contents of nickel, chromium and titanium. The general similarity of the regional average values for these elements suggests that the nephrites have been formed in similar environments. At the 0»Ne-ell Creek deposit in central British Columbia, nephrite occurs in a zone of tremolite-chlorite rock developed in serpentinite at the contact with metasomatically altered sediments. The nephrite has resulted from the metasomatic alteration, by addition of calcium and silica, of the serpentinite during the process of serpentinization. The calcium was derived from the pyroxenes contained in the original ultramafic rock; the source of the silica was the enclosing sediments. High concentrations of calcium and magnesium and relatively lower concentrations of sodium, iron, aluminum and silicon charact• erized the environment in which the nephrite formed. Calcium and sodium were perfectly mobile while the other elements were relatively inert. These condi• tions of mobility and concentration account for the fine fibrous nature of the nephritic tremolite. A temperature range of approximately 300°C to 500°C and a pressure in excess of 4 kilobars are suggested for the formation of the nephrite. (iii) TABLE OF CONTENTS Page ABSTRACT i I. INTRODUCTION 1 NOMENCLATURE AND HISTORY 1 NEPHRITE OCCURRENCES 3 PREVIOUS WORK 4 SCOPE OF PRESENT WORK 5 ACKNOWLEDGMENTS 6 II. BRITISH COLUMBIA DEPOSITS 8 ALPINE ULTRAMAFIC ROCKS OF BRITISH COLUMBIA 9 PLACER OCCURRENCES OF NEPHRITE 11 BEDROCK OCCURRENCES OF NEPHRITE 13 PRODUCTION 15 MINING METHODS 18 MARKETS, PRICES AND USES 19 III. PETROLOGY AND PHYSICAL PROPERTIES OF BRITISH COLUMBIA NEPHRITE 21 NEPHRITE CLASSIFICATIONS 21 Turner Classification 23 Non-schistose Nephrites 23 Schistose Nephrites 23 Semi-nephrites 25 Kalkowsky Classification 25 PETROLOGY 27 Tremolite 27 Chlorite 36 Spinel 38 Ilmenite 38 Diopside 38 Uvarovite 40 Unknown 42 Sphene 42 Carbonate 42 Phlogopite and Talc 42 Pyrite 42 PHYSICAL PROPERTIES 43 Fracture 43 Specific Gravity 43 Colour and Lustre 45 Hardness 46 Crushing Strength and Relative Corrosion Hardness 51 IV. THE CHEMISTRY AND CRYSTALLOGRAPHIC STRUCTURE OF NEPHRITE 52 CHEMISTRY 52 CRYSTALLOGRAPHIC STRUCTURE 57 (iv) Page V. IRON AND TRACE ELEMENT GEOCHEMISTRY OF BRITISH COLUMBIA NEPHRITES 65 DISCUSSION OF RESULTS 69 Iron 69 Cobalt and Nickel 69 Manganese 71 Copper 73 Lead 73 Zinc 73 Chromium, Titanium and Vanadium 75 Element Distribution in Fresh and Weathered Nephrite 76 REGIONAL CHEMICAL VARIATIONS IN BRITISH COLUMBIA NEPHRITES 78 COLOUR OF NEPHRITES 80 VI. THE O'NE-ELL CREEK NEPHRITE DEPOSIT 83 REGIONAL GEOLOGY 83 GEOLOGY OF THE DEPOSIT 88 General Description 88 Lithology 92 Cache Creek Group 92 Trembleur Intrusions 96 Miscellaneous Rock Types 99 Amphibole-zoisite rock 99 Meta-diabase 99 Albite-amphibole rock 99 Meta-aplite 101 Summary 101 PETROGENESIS 102 General Statement 102 Origin of the Nephrite 103 Temperature and Pressure Conditions 109 VII. CONCLUSIONS 111 BIBLIOGRAPHY 113 APPENDIX I Survey of World Deposits 119 APPENDIX II Determinative Methods 132 APPENDIX III Nephrite Analyses Obtained from the Literature 138 (v) ILLUSTRATIONS PLATES Plate Page 1 Scanning electron micrograph of a schistose nephrite 22 transitional to a semi-nephrite illustrating the twisted and interwoven nature of the component tremolite fibers (#37; OtNe-ell Creek), X 300. 2 Scanning electron micrograph of a schistose nephrite 22 transitional to a semi-nephrite illustrating the fine fibrous nature of the tremolite (#37; 0*Ne-ell Creek), X 1270. 3 Photomicrograph of a non-schistose nephrite transitional to 24 a schistose nephrite (#7; Fall River), crossed nicols. 4 Photomicrograph of a schistose nephrite (#10; Kelly Creek), 24 crossed nicols. 5 Photomicrograph of a semi-nephrite, with large sheaves of 26 parallel unfelted fibers (#8$ Fall River), crossed nicols. 6 Photomicrograph of a schistose nephrite transitional to 26 a semi-nephrite (#40; Seywerd Creek), crossed nicols. 7 Photomicrograph of coarse acicular tremolite in a schistose 35 nephrite transitional to a semi-nephrite (#10; Kelly Creek), crossed nicols. 8 Photomicrograph of a radial mass of tremolite fibers set in 35 a fine nephritic base (#45; Dease Lake), crossed nicols. 9 Photomicrograph of an aggregate of chlorite surrounding 37 fragments of chrome spinel (#15; Van Decar Creek), crossed nicols with gypsum plate. 10 Photomicrograph of a fractured chrome spinel grain, 37 partially replaced by chlorite (#15; Van Decar Creek), plane polarized light. 11 Photomicrograph of corroded remnants of diopside 39 (#16; 0»Ne-ell Creek), crossed nicols. 12 Photomicrograph of spindle-shaped diopside crystals 39 (#43; Ogden Mountain), crossed nicols. (vi ) Plate Page 13 Photomicrograph of uvarovite garnet containing corroded 41 grains of chrome spinel (#7; Fall River), plane polarized light. 14 Photomicrograph of anhedral grains of uvarovite garnet 41 (#8; Fall River), plane polarized light. 15 Scanning electron micrograph of a schistose nephrite 60 transitional to a semi-nephrite illustrating the (110) cleavage of tremolite (#37; O'Ne-ell Creek), X 6500. 16 A portion of the nephrite outcrop at O'Ne-ell Creek. 91 17 Photomicrograph of a quartzite from O'Ne-ell Creek, 94 crossed nicols. 18 Photomicrograph of "birds-nesf'-like aggregates of tremo- 94 lite fibers in a quartzite from O'Ne-ell Creek, plane polarized light. 19 Photomicrograph of stilpnomelane (brown) and biotite (green) 95 in fractures in a siliceous argillite from O'Ne-ell Creek, plane polarized light. 20 Photomicrograph of stilpnomelane (brown) and needles of 95 tremolite in an argillite from O'Ne-ell Creek, crossed nicols. 21 Photomicrograph of a serpentinite from O'Ne-ell Creek 98 illustrating the fibro-lamellar structure of the antigor- ite, crossed nicols. 22 Photomicrograph of a quartz-carbonate rock from O'Ne-ell 98 Creek, crossed nicols. FIGURES Figure Page 1 Index map of British Columbia. 10 2 Nephrite production in British Columbia for the period 16 1959 - 1970, inclusive. 3 A graph of Mohs hardness values against the log of Vickers 50 hardness numbers. 4 Curves of weight loss in heating for nephrite and broad- 55 prismatic tremolite from Siberia, U. S. S. R. i (vii) Figure Page 5 MgO-CaO-Fe^O^ + FeO in nephrites from various world local- 56 ities. 6 The structure of tremolite. 58 7 Histograms of the Fe, Co, and Ni contents of British 70 Columbia nephrites. 8 Histograms of the Mn, Cu, and Pb contents of British 72 Columbia nephrites. 9 Histogram of the Zn content of British Columbia nephrites. 74 10 Geology map; Takla Lake-Middle River area, British Columbia. 84 11 Legend for Figure 10. 85 12 Geology; 0»Ne-ell Creek nephrite deposit, O'Ne-ell Creek, In British Columbia. Pocket 13 Diagrammatic representation of mineral zoning at the contact 104 between serpentinite and metasomatized argillite and grey- wacke. 14 Ca (activity) - Si02 (activity) for calcium and magnesium 106 silicates. TABLES Table Page 1 Nephrite production from Mining Divisions, British 17 Columbia. 2 Classification, mineralogy and mode of British Columbia 28 nephrites. 3 Indices of refraction of tremolite in nephrites. 34 4 X-ray diffraction data for kbtschubeite (chromian clino- 36 chlore), clinochlore, kammererite (chromian penninite), pen&inite and for chlorite from British Columbia nephrite specimens.
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