SYNONYMS: Nephrite, nephrite jade, jadestone, greenstone (in New Zealand).
EXAMPLES (British Columbia - Canadian/International): Jade King (092HSW097), Birkenhead (092JNE063), Marshall Creek (092JNE064), Noel Creek (092JNE118), O`Ne-ell Creek (093K 005), Mt. Sidney Willians (093K 043), Mt.Ogden (093N157,165), Wheaton Creek (104I082,085,104), Provencher Lake (104I064,065,066,078,111), Cassiar (104P005) - Yukon, Alaska, Wyoming, California China, Taiwan, New Zealand, Australia, Siberia, Transvaal.
CAPSULE DESCRIPTION: Nephrite is an exceptionally tough, bright green to nearly black massive aggregate of fine grained fibrous amphibole – tremolite or actinolite. Nephrite jade occurs as lenticular bodies. They are associated with serpentinites that are intrusive into or in fault contact with suites of greenstones, chert, pelite and limestone.
TECTONIC SETTING: Alpine type serpentinites, ophiolite complex preceding a formation of island arc. In British Columbia the significant occurrences are found in Bridge River, Southern Cache Creek, Slide Mountain, and Northern Cache Creek terranes.
DEPOSITIONAL ENVIRONMENT / GEOLOGICAL SETTING: The initial geological setting requires the formation of ultramafic rocks that form in proximity of ribbon chert and argillites or are structurally emplaced next to these types of sediments. The ultramafic rocks are frequently associated with regional fault systems where serpentinites are in contact with cherts and siliceous sediment or siliceous intrusive rocks. Subsequent geological processes, in particular serpentinization, is the main factor in forming nephrite jade.
AGE OF MINERALIZATION: Globally, nephrite occurrences are hosted by Precambrian serpentinites in Zimbabwe to Tertiary ultramafic rocks in New Zealand. In B.C. jade is hosted by mid-Pennsylvanian oceanic crustal rocks and Permo-Triassic sediments. Deformation with resulting greenschist metamorphism took place during Middle to Late Jurassic time and was followed by further deformation and dextral strike slip in Late Cretaceous to Early Tertiary. It is thought that the jade formation occurred during the later stages of deformation. At least on some sites, nephrite is contemporary with origin of rodingite.
HOST/ASSOCIATED ROCKS: Serpentinized ultramafic rocks (harzburgite, dunite, pyroxenite) in contact with argillite and cherty sediments. Associated rocks are rodingite and similar heterogeneous calc-silicate rocks (in BC frequently called “whiterock”).
DEPOSIT FORM: Lenticular nephrite bodies typically less than 10 metres wide, 100 metres long at surface occur near contact of major serpentinite mass or in smaller satellite serpentinite slices. In general parallel to the contact with sediments or granitic intrusives and along shear zones.
TEXTURE/STRUCTURE: Massive, very fine grained rock that is light to dark green or almost black in colour. Under the microscope nephrite is characterized by microfibrous tremolite that occurs as interlocking, twisted and felted bundles, tufts and sheaf-like aggregates. Accessory minerals, like magnetite, picotite or garnet, are frequently present in the otherwise fine grained amphibole matrix.
ORE MINERALOGY: Actinolite – tremolite; chromite, magnetite, picotite,uvarovite (chromium garnet).
GANGUE MINERALOGY [Principal and subordinate]: Rodingite – a heterogeneous mixture of zoisite/clinozoisite, serpentine, actinolite/tremolite, wollastonite, prehnite and garnet) / talc, chlorite, sphene, magnetite.
ALTERATION MINERALOGY: Nephrite jade is an alteration product resulting from a metasomatic reaction between serpentinite and a source of silica, usually cherty metasediments.
WEATHERING: Jade is resistant to weathering in contrast to the common host rocks, serpentine and metasediments, and frequently forms boulder trains along its outcrops. Jade may be a common component in alluvial and colluvial deposits.
ORE CONTROLS: Serpentinization of ultramafic rocks in contact with high silica and calcium rocks to produce the formation of tremolite. Key element is large volumes of fluids moving through the serpentinized ultramafics capable to produce the metasomatic reaction with chemically right environment.
GENETIC MODELS: The studies on serpentinites indicate, that nephrite is a result of the desilication and calcium metasomatism produced in contact of serpentinites with sedimentary rocks under close to the blueschist metamorphic conditions.The reaction zone develop at a time when larger masses of ultramafic mantle are tectonically emplaced into the base of the crust or moved tectonically higher into it. This may produce a metasomatic reaction resulting in nephrite lenses surrounded by tremolite/chlorite alteration zone (usually called "whiterock"). Ultramafic rock must be below olivine stability field for the reaction to occur. Monomineralic and fine grained jade is stable in a variety of thermodynamic conditions. Evidence is pointing to conclusion, that nephrite jade forms during highly dynamic tectonic activity with fast changing local conditions in temperature, pressure and circulating fluids. Formation of nephrite is considered to occur at temperatures between 500ºC and 290ºC with pressure between 4 and 8 Kb where the water pressure was nearly equal to the total pressure.
ASSOCIATED DEPOSIT TYPES: Ultramafic hosted talk-magnesite (M07), ultramafic hosted asbestos (M06). The Cassiar asbestos deposit produced jade periodically as a by-product.
COMMENTS: There are two types of jade - nephrite and jadeite. While nephrite jade is mineralogically a variety of amphibole, jadeite is a variety of pyroxene. All known Canadian jade occurrences are the nephrite variety.
GEOCHEMICAL SIGNATURE: Not normally used.
GEOPHYSICAL SIGNATURE: Magnetic highs can be used to identify ultramafic and serpentinite bodies.
OTHER EXPLORATION GUIDES: Prospecting for boulder trains and boulders in creeks. The boulders typically have a smooth surface and need to be broken or drilled to see the jade quality. Presence of “whiterock” or rodingite in serpentine outcrop.
TYPICAL GRADE AND TONNAGE: Grades depend on colour, impurities, and presence of fractures. The highest quality jade has a uniform bright green translucent colour (emerald) with little or no impurities and limited fractures. Also the stone`s fabric, i.e. orientation of individual grains is important. In situ deposits range in size from a few tonnes to more than 4000 tonnes, although not all of the deposit will be commercial jade. Jade cobbles and boulders are also exploited and can be up to tens of tones in weight.
ECONOMIC LIMITATIONS: Top grade jade (without flaws and of good colour) is routinely flown out to the nearest good road, otherwise road access is required. Non-standard colours can come into vogue at times.
END USES: Semiprecious stone used for carving, tiles and ornamental applications. In primitive cultures, jade has been used for weapons, tools and gemstones. Some cultures particularly value jade as a precious stone like Chinese, Maori in New Zealand or Maya Indians in Mexico and Guatemala.
IMPORTANCE: Annual exports of B.C. jade are approximately 100 to 200 tonnes. In 1991, a 32 tonne jade boulder was sold for $CDN 350,000 to be carved into a Buddha statue in Thailand. In 1996 the best quality raw jade sold for $100 per kilogram. Most of the jade produced in British Columbia is regularly exported to Far East countries, some to New Zealand. BC is leading world exporter of nephrite jade.
Coleman, R. (1967): Low-Temperature Reaction Zones and Alpine Ultramafic Rocks of California, Oregon and Washington. U.S.Geological Survey, Bulletin 1247, 49 pages.
Fraser, M. (2000): Nephrite Jade; Western Canadian Gemstone Newsletter, Winter 2000 Edition, Volume 2, Number 1, 5 pages.
Gunning, D.F. (1995): Exploring British Columbia`s Stone Industry; Stone World, Volume 12, Number 10, pages 40-50.
Holland, S.S. (1961): Jade in British Columbia; British Columbia Minister of Energy, Mines and Petroleum Resources, Annual Report for the Year 1961, pages 119-126.
Keverne, R., Editor (1995): Jade; Lorenz Books, London, UK, 376 pages.
Leaming, S.F. (1984): Jade in British Columbia and Yukon Territory, in Guillet, G.R. and Martin, W., The Geology of Industrial Minerals in Canada, The Canadian Institute of Mining and Metallurgy, Special Volume 29, pages 270-273.
Leaming, S.F. (1978): Jade in Canada, Geological Survey of Canada, Paper 78-19, 59 pages.
Makepeace, K. and Simandl, G.J. (2004): Jade (Nephrite) in British Columbia, Canada;in G.J.Simandl, W.J.McMillan and N.D.Robinson, Editors, 37th Annual Forum on Industrial Minerals Proceedings, Industrial Minerals
with emphasis on Western North America,British Columbia Ministry of Energy and Mines, Geological Survey Branch, Paper 2004-2, pages 287-288.
Scott, A. (1996): Jade. The Mystical Mineral; Equinox, Number 89, September/October 1986, pages 63-69.
Simandl, G.J., Riveros, C.P. and Schiarizza, P. (2000): Nephrite (Jade) Deposits, Mount Ogden Area, British Columbia (NTS 093N 13W); British Columbia Ministry of Energy, Mines and Petroleum Resources, Paper 2000-1, pages 339-347.
Simandl, G.J., Paradis, S. and Nelson, J. (2001): Jade and Rhodonite Deposits, British Columbia, Canada; in Proceedings of the 34th Forum on Industrial Minerals, Salt lake City (1998); Utah Geological
Survey Miscellaneous Publication 01-2, pages 163 – 171.
Thompson, B., Brathwaite, B. and Christie, T. (1995): Mineral Wealth of New Zealand; Institute of Geological and Nuclear Scienes Limited, Information Series 33, 170 pages.
Ward, F. (1987): Jade. Stone of Heaven; National Geographic, Volume 172, Number 3, pages 282-315.
by Z.D. Hora
Retired, British Columbia Geological Survey, Victoria, B.C., Canada
SYNONYMS: Manganese spar, manganolite (pyroxmangite)
COMMODITIES/BY-PRODUCTS: Rhodonite / jasper
EXAMPLES (British Columbia - Canadian/International): Hill 60 (092B 027), Hollings (092B 074), Rocky (092C 113), Arthur Point (092M015), Clearcut (082ESE241), OrofinoMtn (082ESW009), Olalla (082ESW017), Ashnola Pinky (082ESW208), Joseph Creek (092P148), Snowy Creek (104P067), / Evelyn Creek (Yukon).
CAPSULE DESCRIPTION: Lenses of bedded or massive rhodonite hosted by laminated cherts and cherty tuffs at the base of turbiditic sandstone, siltstone and argillite sequences, usually in proximity to mafic volcanics or greywackes. Red jasper beds with laminated hematite, pyrite and magnetite are sometimes associated with deposits of rhodonite.
TECTONIC SETTING: Island arcs, back arc basins, sea floor spreading areas. Epicratonic or continental margin marine basins associated with oceanic faults or rifts.
DEPOSITIONAL ENVIRONMENT / GEOLOGICAL SETTING: Deep to shallow marine basins. The widespread soft-sediment structures present in the host rock and within the rhodonite bodies suggest deposition of an unstable, gel-like sediment. Submarine hydrothermal activity in mafic environment, abundant silica to feed radiolarian population in the area. Similar modern environments have been described from the Galapagos, southwest Pacific island arc, Gulf of Aden and Mid-Atlantic Ridge.
AGE OF MINERALIZATION: In British Columbia described as mostly Mississippian, Carboniferous or Permian in age, also Upper Triassic. Recently found in a Lower Cretaceous unit. Globally, this type probably may occur in oceanic units of any age.
HOST/ASSOCIATED ROCKS: Ribbon cherts, laminated cherts and cherty tuffs with argillite interbeds; pillow basalts, mafic tuffaceous sediments and greywacke turbidites in the lower part of sequence; sandstone, argillite, calcarenite and limestone in the upper part. Rhodonite is also found in the metamorphosed equivalents of these rocks; typically prehnite-pumpellyite to greenschist grade.
DEPOSIT FORM: Stratiform lenses of rhodonite that are metres thick and intermittently extend laterally some hundreds of metres. Frequently discontinuous and pinching out over tens of metres or less. Thin rhodonite bands less than 10 centimetres across often pinch out over several metres. Thicker rhodonite layers can be followed for distances of more than 50 metres.
TEXTURE/STRUCTURE: The texture of rhodonite varies from laminated to patchy. Massive rose-pink layers alternate with darker bands and minor yellow and grey chert. Soft sediment deformation features are frequent, particularly along the hanging wall of major rhodonite lenses. Embedded fragments of roof sediment in chert rhodonite and small "ghost" radiolarians infilled by microcrystalline quartz are common. Crosscutting and bedding parallel rhodonite veinlets up to a few millimetres thick are typical. Some rhodonite lenses adjacent to footwall contain layers and round shaped metallic, black nodules of braunite (Mn,Si)2O3 from 5 to 10 millimetres in diameter that are overgrown with
concentric pink rhodonite rims. The predominant minerals in massive rhodonite-rich zones are usually microcrystalline quartz interbedded with disseminated, mottled and banded rhodochrosite and rhodonite, interlayered with hematite and garnet-rich bands. Manganese oxide is invariably present lining hairline fractures and as surface coatings. Rhodonite occurs as intergrowths with massive or crystalline rhodochrosite as euhedral elongate tabulate crystals, stellated crystal masses or sheath-like bundles enclosed within and encroaching upon a microcrystalline quartz matrix. Rhodonite also forms spongy porphyroblasts up to 500 microns in length. Some rhodonite exhibits mammillary growth textures. Rhodochrosite ranges from a massive carbonate to a mixture of with microcrystalline quartz, rhodonite or disseminated hematite. At higher metamorphic grades the rhodonite exhibits more granoblastic to porphyroblastic texture.
ORE MINERALOGY [Principal and subordinate]: Rhodonite, rhodochrosite, pyroxmangite / microcrystalline silica, barite, spessartine garnet, bustamite, tephroite, palenzonaite, penninite, clinochlore, stilpnomelane, adularia.
GANGUE MINERALOGY [Principal and subordinate]: Jasper, chert and manganese oxide / argillite interbeds.
ALTERATION MINERALOGY: Effects of metamorphism: amphibole, graphite, phlogopite, garnet, plagioclase in higher metamorphic grades; garnet - tremolite – adularia – prehnite - epidote quartz association in lower metamorphic grades.
WEATHERING: Widespread development of black oxidized manganese secondary products as veinlets, on fractures and coating surfaces.
ORE CONTROLS: The primary control on rhodonite deposits are a favourable stratigraphic package of deep water marine sedimentary and volcanic rocks with a significant sequence of cherts containing manganese-rich layers. Secondary controls are synsedimentary and later deformation that can create thicker or thinner lenses and later processes, such as cross-cutting veinlets, that reduce the value of the rhodonite or rhodochrosite.
GENETIC MODELS: Manganese is deposited as a distal member of volcanogenic products from hydrothermal solutions generated in rifting environment where the thermal fluids percolated through sea-floor basalts and associated rocks of similar chemical composition. These solutions would be hot, slightly acid, strongly reducing, and enriched in Mn, Fe, Si, Ba, Ca, K, Li, Rb and trace metals. Separation of Fe from Mn may occur within the seafloor at depth with the formation of sulphides like pyrite and on the seafloor when the hydrothermal solution mixed with cold, alkaline and oxygenated seawater and precipitated chemical sediments. Nucleation and precipitation kinetics of Mn and Si oxides are sluggish; therefore, they are often distributed distally from the hydrothermal vent. At lower temperatures the manganese precipitates as amorphous oxyhydroxides and Mn4+ oxides, moderately
higher temperatures could promote syndepositional Mn silicate and carbonate. The hydrothermal sediments can form mounds and retain level of semi-plasticity for extended time which can lead to synsedimenatary deformation and slumping. Alternatively, Mn silicate and carbonate may form during subsequent diagenetic or metamorphic episodes.
ASSOCIATED DEPOSIT TYPES: Red jasper with taconite iron mineralization (G01), all manganese oxide deposits associated with volcanogenic origin (G02) and volcanogenic massive sulphides (G04, G05, G06).
COMMENTS: The name "Rhodonite" is rather a misnomer. The rock is a mixture of pink manganese silicates and a carbonate with fine grained silica. There are many manganese deposits described from all parts of world that are considered of volcanogenic origin. Deposits of rhodonite outside of the Canadian Cordillera are rather uncommon. One possible explanation is that glaciation may have exposed primary deposits which could be deeply weathered with a thick zone of manganese oxides in non-glaciated areas.
GEOCHEMICAL SIGNATURE: Anomalous in manganese, enriched in base metals, barium and strontium.
GEOPHYSICAL SIGNATURE: Not used, probably reflecting the small size of the orebodies and similarities to the associated chert.
OTHER EXPLORATION GUIDES: Oceanic terrains, chert beds, particularly with red jasper, and black staining.
TYPICAL GRADE AND TONNAGE: Lenses from up to 3 metres thick and 15 metres long on surface. In most economic deposits, rhodonite and rhodochrosite account for at least 45% of the lens.
However, rock hounds often contribute some supply from lenses with lower contents of the semi-precious stone. Two properties in Western Canada were active producers for 20 years – one in Yukon and the other on the British Columbia coast. After the initial major production period, both have been largely inactive for more than 10 years.
ECONOMIC LIMITATIONS: Physical/chemical properties affect the end use. Brighter colours due to rhodochrosite and attractive dendrite black veining increase aesthetic value. Dense fracturing decreases the value and uncemented microfractures restrict carving of larger statues. The relatively high unit value for rough rhodonite allows for processing far away from the original source, frequently overseas.
END USES: Semiprecious stone used in lapidary, jewellery and carvings.
IMPORTANCE: The North American market is very small - only a few tonnes annually. Semi-precious stone used to produce jewellery and carvings. The industry considers rhodonite as a potential substitute for pink coral when environmental considerations prevent its production.
Cowley, P. (1979): Correlation of Rhodonite Deposits on Vancouver Island and Saltspring Island, British Columbia, Bachelor thesis, Department of Geological Sciences, The University of British Columbia, 54 pages.
Crerar, D.A., Namson,J., Chyi, M.S., Williams, L. and Feigenson, M.D. (1982): Manganiferous Cherts of the Franciscan Assemblage: I. General Geology, Ancient and Modern Analogues, and Implications for Hydrothermal Convection at Oceanic Spreading Centers, Economic Geology, volume 77, Number 3, pages 519-540.
Danner, W.R. (1976): Gem Materials of British Columbia, in Montana Bureau of Mines and Geology, Proceedings Volume, Eleventh Forum on the Geology of Industrial Minerals, Special Publication 74, pages 156-169.
Flohr, M.J.K. (1992): Geochemistry and Origin of the Bald Knob Manganese Deposit, North Carolina, Economic Geology, volume 87, pages 2023-2040.
Flohr, M.J. and Huebner, J.S., (1990): Microbanded Manganese Formations: Protoliths in the Franciscan Complex, California, U.S. Geological Survey, Professional Paper 1502, 72 pages.
Glasby, G.P. (1977): Marine Manganese Deposits, Elsevier Scientific Publishing Company, Amsterdam, 465 pages.
Hancock, K.H. (1992): Arthur Point (Sea Rose) Rhodonite, Ministry of Energy, Mines and Petroleum Resources, Exploration in British Columbia 1991, pages 89-98.
Hora, Z.D. (1988): Industrial Minerals in Island Arcs, in Metallogeny of Volcanic Arcs, BC Ministry of Energy, Mines and Petroleum Resources, Short Course Notes, Open File 1998-5, section B, pages L1-L41
Hora, Z.D., Langrova, A. and Pivec, E.(2005): Contribution to the Mineralogy of the Arthur Point Rhodonite Deposit, Southwestern British Columbia; in Geological Fieldwork 2004, BC Ministry of Energy, Mines and Petroleum Resources, Paper 2005 – 1, pages 177-185.
Hora, Z.D., Langrova, A. and Pivec, E. (2007): Rhodonite from the Bridge River Assemblage, Downton Creek (NTS 092J/09), Southwestern British Columbia; in Geological Fieldwork 2006, BC Ministry of Energy, Mines and Petroleum Resources, Paper 2007-1, pages 39 – 43.
Leaming, S.F. (1966): Rhodonite in British Columbia, The Canadian Rockhound, pages 5-11.
Massey, N.W.D. (1992): Geology and Mineral Resources of the Duncan Sheet, Vancouver Island 92B/13, B.C. Ministry of Energy, Mines and Petroleum Resources, Paper 1992-4, 112 pages.
Nelson, J.A., Hora, Z.D., and Harvey-Kelly, F. ( 1990): A New Rhodonite Occurrence in the Cassiar Area, Northern British Columbia (104P/5), B.C. Ministry of Energy, Mines and Petroleum Resources, Geological Fieldwork 1989, Paper 1990-1, pages 347-350.
Sargent, H. (1956): Manganese Occurrences in British Columbia, in J.G.Reyna, Editor, Symposium Sobre Yacimientos de Manganeso, XX Congreso Geologico Internacional, Mexico, Tomo III., pages 15-34.
Simandl, G.J. and Church, B.N. (1996): Clearcut Pyroxmangite/Rhodonite Occurrence, Greenwood Area, Southern British Columbia (82/E2), in Geological Fieldwork 1995, BC Ministry of Energy, Mines and Petroleum Resources, Paper 1996-1, pages 219-222.
Simandl, G.J., Hancock, K.D., Nelson, J.A., and Paradise, S. (1997): Rhodonite Deposits in British Columbia, Canada, Canadian Institute of Mining and Metallurgy, Annual Meeting, Paper CIM MPM2-F3, abstract.
Simandl, G.J., Paradis, S. and Nelson, J. (2001): Jade and Rhodonite Deposits, British Columbia, Canada; in Proceedings of the 34th Forum on Industrial Minerals, Salt Lake City (1998), Utah Geological
Survey, Miscellaneous Publication 01-2, pages 163 – 171.
Snyder, W.S. (1978): Manganese Deposited by Submarine Hot Springs in Chert-Greenstone Complex, Western United States, Geology, volume 6, pages 741-744.
Sorem, R.K. and Gunn, D.W. (1967): Mineralogy of Manganese Deposits, Olympic Peninsula, Washington, Economic Geology, volume 62, pages 22-56.