Jade Deposits
Jade Deposits
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Jade Deposits
Nephrite is considered to be a product of metasomatism and alteration, generally associated with gneisses, serpentinites, schists (especially hornblende schists), and metamorphosed limestones or dolomites. It occurs as sheets, lenses, and nodules along or near contacts between dissimilar rock types in strongly metamorphosed zones, and in or adjacent to faults and fault zones.
Wyoming nephrite occurs within granitic gneisses, usually in close association with intruded amphibolites, shear zones, faults, and local folds or otherwise distorted and broken rock. The rock has invariably been re-cemented by quartz, nephrite, or other minerals related to fluid movement. Wall rock alteration accompanies nephrite development, bleaching adjacent granite-gneiss and resulting in a characteristic appearance. Typically, this includes a mottled pink and white granite-gneiss with associated secondary clinozoisite, pink zoisite, epidote, chlorite, and white plagioclase pervasively altered to mica.
Map showing general areas of reported occurrences of in-place nephrite veins and detrital jade.
Deep apple-green Wyoming Jade. [Credit: Wayne M. Sutherland, WSGS]
Sherer (1969) suggested Wyoming nephrite deposits developed from hydrous metasomatic alteration of amphibole during metamorphism. Iron, aluminum, and calcium mobilization accompanied this process to result in epidotization of surrounding country rocks, which may be extensive.
Amphibole, primarily hornblende, reacted with hot metamorphic fluids to produce actinolite-tremolite (nephrite jade), clinozoisite, and chlorite. This alteration concentrated along shear zones and fractures where it resulted from the emplacement of quartz diorite, vein quartz, or pegmatite.
Sherer (1969) hypothesized that water loss at sites of nephrite development stopped the alteration process that would have otherwise continued to convert nephrite into serpentine. Harlow and Sorensen (2001) suggested that the felted fibrous masses characteristic of nephrite derived from supersaturation of interacting fluids at low temperatures but acknowledge alternate possibilities.
Timing of Nephrite Development
Timing of Nephrite Development
Interpretation of the geologic history of the Granite Mountains and the timing of events related to nephrite development is based on investigations by numerous individuals. These include D.A. Bagdonas, K.R. Chamberlain, C.D. Frost, B.R. Frost, B.L. Fruchey, R.L.B. Grace, G.D. Langstaff, and E.N. Wall, noted in the references at the bottom of the page.
Most primary nephrite deposits in Wyoming appear to be related to Archean structures consistent with continental collision and accretion in a zone referred to by some as the Oregon Trail structural belt. The Oregon Trail structural belt extends eastward from the Wind River Mountains to the northern Laramie Mountains. This structure documents where Archean rocks to the south were accreted onto the Wyoming Craton to the north approximately 2.65 to 2.63 Ga (Ga = billion years ago). Numerous pervasive, dominantly ductile, east- to northeast-trending shear zones with steep southerly dips cut Archean rocks in this region.
The Granite Mountain batholith intruded the area around 2.62 Ga and is considered by Bagdonas (2014) to be part of the much larger Wyoming Batholith that extends westward into the southern Wind River Mountains and eastward into the Laramie Mountains. East- to northeast-trending mafic dikes intruded rocks of the Granite Mountains during two intervals at approximately 2.6 to 2.4 Ga and 1.47 to 1.45 Ga.
The first radiometric dating of nephrite in the Granite Mountains was by Peterman and Hildreth (1978). They obtained a piece of massive nephrite from a 10-cm-wide vein, which yielded 39Ar/40Ar dates of 2,460 ± 45 and 2,560 ± 45 Ma that they averaged to give an age of 2,510 ± 35 Ma (Ma = million years ago). They concluded diabase veins and nephrite deposits were both emplaced shortly after the intrusion of the Lankin Dome Granite, which they dated at 2,550 ± 60 Ma. More recent radiometric dating has refined the age of the Lankin Dome Granite at 2.62 Ga and the more extensive Wyoming Batholith at approximately 2,625 Ma.
Nephrite formation in central Wyoming is interpreted to be coincident with epidote formation adjacent to the nephrite deposits. Kevin Chamberlain (personal commun., 2014) dated epidotes associated with alteration zones surrounding Wyoming nephrite deposits from three different locations. One sample indicated progressive epidote growth from 2,477 to 2,462 Ma, while another indicated progressive growth from 2,550 to 2,520 Ma. A third location with a broad alteration zone yielded an age of 2,475 ± 11 Ma. This suggests that there may have either been two extended periods of epidote growth ca. 2,550 to 2,520 Ma and 2,477 to 2,460 Ma, or a much longer period extending from 2,550 to 2,460 Ma. The 2,550–2,520 Ma period is coincident with the intrusion of late magnetite-bearing plutons in the region (Chamberlain, personal commun., 2014), although the dominant period of regional plutonism occurred at about 2,625 Ma. General relationships suggest that nephrite and epidote are both either coeval with or post-date plutonism.
Alteration Zones
Alteration Zones
Although typical alteration zones accompany many Wyoming nephrite deposits, numerous jade veins have been observed with little or no accompanying alteration zones. This suggests that the hydrous fluids responsible for the jade at such locations reacted with the surrounding rocks only slightly or not at all. Jade, differentiated from actinolite-tremolite by jade’s microcrystalline structure, must have crystallized relatively rapidly at such sites from fluids supersaturated with actinolite-tremolite. The overall character of the host fluid must also have changed to prevent alteration of the surrounding rock. This may have resulted from either a rapid decrease in temperature or pressure, or both.
In contrast, some areas with wide alteration zones typical of nephrite deposits are known to host only low-quality nephrite or macroscopic crystals of actinolite-tremolite. Such areas likely had relatively slow changes in temperature and pressure that allowed larger crystal growth and greater penetration of the surrounding rocks by fluids.
Fine-grained, dark-green nephrite surrounds an aggregate of partially eroded, euhedral quartz crystals. [Credit: Wayne M. Sutherland, WSGS]
Typical aggregate of euhedral quartz crystals deposited from hydrous fluids in an open void. [Credit: Wayne M. Sutherland, WSGS]
Some of the highest quality jade is found surrounding large clusters of well-formed quartz crystals. The form of the quartz is typical of radiating crystals deposited on the walls of voids from hydrous fluids; these crystals are interpreted to have such an origin. The large size of the quartz crystals and absence of chalcedony suggests relatively slow and uniform quartz crystal growth in at least a temporarily stable environment. Some specimens are noted where high-quality nephrite surrounds brecciated quartz crystals, suggestive of an unstable environment in which nephrite was rapidly crystallized.
As with other geologic phenomena, there are variations. High-quality jade may surround quartz crystals with no perceptible alteration of the quartz; perhaps very rapid jade precipitation occurred due to an almost catastrophic change in temperature and pressure. Some quartz-jade interfaces show shallow alteration of the quartz crystals; these may have had slightly longer contact with the nephrite-bearing fluid before its crystallization. Some jade of lesser quality shows an almost complete replacement of quartz (and occasionally other minerals) crystals, leaving “ghost crystals” within the jade.
Many pieces of detrital jade have been found with the well-formed impressions of quartz crystals. The quartz was presumably removed from the jade during weathering. Some highly weathered, in-place “should-have-been nephrite” deposits are marked only by chalky-white to gray-green, relatively soft actinolite-tremolite surrounding well-formed quartz crystals.
Quartz crystal remnant and quartz crystal impression within medium-green nephrite. [Credit: Wayne M. Sutherland, WSGS]
In consideration of the above observations, it is possible that fluids related to batholith emplacement interacted with amphiboles to produce hydrous fluids supersaturated with actinolite-tremolite. Fluid chemistry was probably variable with time, location, and incident rock types. The active continental collision zone of the Oregon Trail structural belt most likely provided tectonic fractures as conduits for fluid movement. Such conduits would open or close in concert with tectonic activity, allowing either rapid entry or slow infusion of various hydrous fluids.
Thin vein of high-quality light-apple-green nephrite cutting lower-quality medium-green nephrite. [Credit: Wayne M. Sutherland, WSGS]
Slow infusion of fluids into these conduits would allow deep reactions with surrounding rocks resulting in wide alteration zones and relatively slow growth of quartz or actinolite-tremolite crystals. If these slow growth deposits remained within a temperature-pressure environment similar to that in which they formed, alteration processes would continue, resulting in serpentine or other end products. However, rapid entry of fluids into such conduits would allow fluids to ascend to cooler temperatures and lower pressures, where rapid precipitation from supersaturated fluids would produce the random microcrystalline structures found in nephrite jade.
Continuous sporadic uplift associated with continental collision could provide the necessary conditions for both formation of nephrite and its preservation. The process of jade formation apparently repeated erratically over time. This repetition is demonstrated where one type of nephrite deposit is cut by later veins of a different character.
Wyoming host rocks for detrital jade in central Wyoming.
Irregular surface of a naturally polished, dark-green jade slick with small spots of a reddish weathering rind. [Credit: Wayne M. Sutherland]
Detrital Jade Deposits
Detrital Jade Deposits
Erosion of the core of the Granite Mountains subsequent to their uplift in the earliest Eocene produced thick conglomerates, primarily to the south. These conglomerates held boulders and cobbles of nephrite jade that had been tumbled for many miles. That tumbling broke up and destroyed much of the less resistant rock types and low-quality jade. Later during the Pliocene, the Granite Mountains were down-dropped, resulting in an accompanying reversal of stream flows to the north and further destruction of weaker rocks. Chemical and mechanical weathering further reduced less durable rocks and left a surface with an enhanced concentration of resistant rock, such as jade. Erosion of the Laramie and Wind River mountains similarly resulted in detrital jade deposits, but of lesser extent.
High-quality nephrite was found in residual and alluvial deposits as rounded boulders and cobbles during the early years of jade hunting. Although 80 years of intense jade hunting has removed most of the easily observable detrital jade, occasional finds, mostly of small pieces, are still made. The Eocene Ice Point Conglomerate, southeast of Sweetwater Station, at one time hosted relatively common boulders of apple-green, pink, and black nephrite jade. The Eocene Crooks Gap Conglomerate hosted apple-green jade boulders, but these were not abundant. Jade pebbles and cobbles have also been found in the Eocene Wind River, Battle Springs, and Wagon Bed formations. Similarly, jade has been found in the Oligocene White River, Oligocene-Miocene Split Rock and the Miocene-Pliocene Moonstone formations. Quaternary terrace, pediment, and alluvial fan gravels, as well as alluvium along modern drainages have also hosted detrital jade.
Nephrite may take on a natural polish from fluvial abrasion and from wind-driven sand in desert areas such as the Granite Mountains. Naturally polished pieces of nephrite jade exhibit a high-gloss, waxy surface and are known as jade slicks. When not in the form of slicks, nephrite pieces may be covered with a cream to reddish-brown oxidized weathering rind that hides the jade’s true color. Experienced jade prospectors learn to recognize this weathered surface and can often recognize jade that others have overlooked.
Wyoming Jade References and Recommended References
Wyoming Jade References and Recommended References
Recommended Jade Reference Material
Further information about Wyoming Jade can be found in the following WSGS publications:
For a complete listing of WSGS materials, go to the Online Catalog.
Jade References
Bagdonas, D.A., 2014, Petrogenesis of the Neoarchean Wyoming batholith, central Wyoming: Laramie, University of Wyoming, M.S. thesis, 120 p., 1 pl.
Barnes, L.C., Flint, D.J., and Dubowski, T., 1987, World review of nephrite jade—Geology, production, and reserves: South Australia Department of Mines and Energy, Rept. Bk. No. 87/116, 48 p., 12 tables, 6 figs.
Bauer, Max, 1969, Precious Stones: Charles E. Tuttle Company, Rutland, VT, and Tokyo, Japan, 647 p.
Bergsten, L.J., 1964, History of the Wyoming Jade region: Lapidary Journal, September 1964, Reprinted in MacFall, Russell P., ed., undated, Wyoming Jade—A Pioneer Hunter’s Story: Self published, 56 p.
Bishop, D.T., 1964, Retrogressive metamorphism in the Seminoe Mountains, Carbon County, Wyoming: Laramie, University of Wyoming, M.S. thesis, 49 p., scale 1:24,000.
Branham, A., 1941, Jade found in Wyoming: The Mineralogist, v. 9, no. 3, p. 79–80.
Branham, A., 1965 and 1966, Several articles in MacFall, Russell P., ed., undated, Wyoming Jade—A pioneer hunter’s story: Self published, 56 p.
Chamberlain, K.R., and Frost, B.R., 1995, Mid-Proterozoic mafic dikes in the central Wyoming Province—Evidence for Belt-age extension and supercontinent breakup: Geological Association of Canada—Mineralogical Association of Canada annual conference, Abstracts, v. 20, p. A-15.
Chamberlain, K.R., Frost, C.D., and Frost, B.R., 2003, Early Archean to Mesoproterozoic evolution of the Wyoming Province – Archean origins to modern lithospheric architecture: Canadian Journal of Earth Sciences, v. 40, no. 10, p. 1,357–1,374.
Chamberlain, K.R., Sears, J.W., Frost, B.R., and Doughty, P.T., 2000, Ages of Belt Supergroup deposition and intrusion of mafic dikes in the central Wyoming Province—Evidence for extension at ca. 1.5 Ga and 1.37 Ga and potential piercing points for Rodinia reconstructions: Geological Society of America, Abstracts with Programs, v. 32, no. 7, p. A-319.
Dake, H.C., 1942, Jade in Wyoming—New discoveries: The Mineralogist, v. 10, no. 9, p. 275–276.
Frost, C.D., Frost, B.R., Chamberlain, K.R., and Hulsebosch, T.P., 1998, The Late Archean history of the Wyoming Province as recorded by granitic magmatism in the Wind River Range, Wyoming, Precambrian Research, v. 89, p. 145–173.
Frost, C.D., Fruchey, B.L., Chamberlain, K.R., and Frost, R.B., 2006, Archean crustal growth by lateral accretion of juvenile supracrustal belts in the south-central Wyoming Province: Canadian Journal of Earth Sciences, v. 43, p. 1,533–1,555.
Fruchey, B.L., 2002, Archean supracrustal sequences of contrasting origin—The Archean history of the Barlow Gap area, northern Granite Mountains, Wyoming: Laramie, University of Wyoming, M.S. thesis, 178 p., scale 1:24,000 and 1:3,000.
Grace, R.L.B., Chamberlain, K.R., Frost, B.R., and Frost, C.D., 2006, Tectonic histories of the Paleoarchean to Mesoarchean Sacawee block and Neoarchean Oregon Trail structural belt of south-central Wyoming Province: Canadian Journal of Earth Sciences, v. 43, no. 10, p. 1,445–1,466..
Harlow, G.E., and Sorensen, S.S., 2001, Jade: Occurrence and metasomatic origin—Extended abstract from International Geological Congress 2000: The Australian Gemmologist, v. 21, p. 7–10.
Hausel, W.D., and Holden, G.S., 1978, Mineral resources of the Wind River Basin and adjacent Precambrian uplifts: Wyoming Geological Association 13th Annual Field Conference, Guidebook, p. 303–310.
Hill, Robert Sr., 1979, Nephrite, jadeite—jade: Gems & Minerals Magazine, no. 504, p. 62.
Hurlbut, C.S., and Switzer, G.S., 1979, Gemology: John Wiley & Sons, New York, NY, 252 p.
Kraft, J.L., 1947, Adventure in jade: Holt and Company, 81 p.
Langstaff, G.D., 1995, Archean geology of the Granite Mountains: Golden, Colorado School of Mines, Ph.D. dissertation, 671 p., 9 pls., scale 1:24,000 and 1:100,000.
Love. J.D., 1945, Jade deposits in central Wyoming: Unpublished partial draft, 5 p.
Love. J.D., 1970, Cenozoic geology of the Granite Mountains area, central Wyoming: USGS Professional Paper 495-C, p. C1-C154, scale 1:125,000.
Ludwig, K.R., and Stuckless, J.S., 1978, Uranium-lead isotope systematics and apparent ages of zircons and other minerals in Precambrian granitic rocks, Granite Mountains, Wyoming: Contributions to Mineralogy and Petrology, v. 65, p. 243-254.
MacFall, R.P., ed., undated, Wyoming Jade—A Pioneer Hunter’s Story: Self-published, 56 p.
Madsen, M.E., 1978, Nephrite occurrences in the Granite Mountains region of Wyoming: Wyoming Geological Association 13th Annual Field Conference Guidebook, p. 393–397.
Peterman, Z.E., and Hildreth, R.A., 1978, Reconnaissance geology and geochronology of the Precambrian of the Granite Mountains, Wyoming: U.S. Geological Survey Professional Paper 1055, 22 p.
Rhoads, Verla, 1969, History on Wyoming Jade: unpublished, 6 p.
Sanders, G.V., 1945, Green gold of Wyoming: Popular Science, v. 146, no. 2, p. 112–114, 208.
Sherer, R.L., 1969, Nephrite deposits of the Granite, Seminoe, and Laramie mountains, Wyoming: Laramie, University of Wyoming, Ph.D. dissertation, 194 p., 30 pls.
Sinkankas, John, 1959, Gemstones of North America: Van Nostrand Company, Inc., New York, NY, 675 p.
Sutherland, W.M., 2010, The discovery of Wyoming Jade: Jade State News, v. 2010, is. 2, p. 2–3.
Wall, E.N., 2004, Petrologic, geochemical and isotopic constraints on the origin of 2.6 Ga post-tectonic granitoids of the central Wyoming Province: Laramie, University of Wyoming, M.S. thesis, 185 p.
Ward, F., 1999, World jade resources: Arts in Asia, v. 29, no. 1, p. 68–71, in Gemological Abstracts, Gems and Gemology, Summer 1999, v. 35, no. 2, p. 163.
Ward, F., 2001, Jade: Gem Book Publishers, Bethesda, MD, 64 p.
Contact:
Christopher Doorn, christopher.doorn@wyo.gov
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