Virtual Museum ID: 19-BCGS-BKDGV1
The color in amethyst from most localities is unevenly distributed in the individual crystals. In amethyst geodes, it is often most intense in the growth zones under the rhombohedral faces (at the tips). Occasionally the color is deeper under either the r or z rhombohedral faces, giving the crystal a pinwheel appearance when viewed from the top. In prismatic crystals, the color may appear in phantom-like thin layers, while in scepters and skeleton quartz the color is often concentrated along the edges, and accompanied by smoky zones. Despite the intense color, the content of iron occupying Si positions in amethyst is rather low, in the 10-100 ppm range (Dennen and Puckett, 1972).
When heated to more than about 300-400°C, amethyst loses its violet color and often turns yellow, orange or brown, and then resembles the quartz variety citrine, but depending on the locality and the temperature during the heat treatment it may also turn colorless or - rarely - green (Rose and Lietz, 1954; Neumann and Schmetzer, 1984).
The information listed below relates to the current holding location or collection that the sample is from, and whether the item is viewable at that location or is part of a private collection. Coordinates are given as guides, and we remind you that collecting specimens from these locations is not allowed. Caution is advised visiting such sites and Below BC assumes no responsibility for any injuries or trespassing charges that may occur as a result of the viewer entering these sites.
Original Collection:British Columbia Geological Survey (BCGS)
Virtual Museum ID:19-BCGS-BKDGV1
Date Added to VM:2019-05-07
Sample Origin:Blackdome Mountain, B.C.
Specific Site:Blackdome Property
Datum:10 (NAD 83)
Primary Mineral Formula:SiO2
Advanced Geological Information
The following section provides geological data relating to the specimen or the site it was collected from, when available. Information has been obtained from various sources including private and government datasets but may not be up to date. Any geological time periods or ages listed often relate to the primary geology of the area, and may not be the actual date of an event such as mineral formation.
Geological Period:Early- Middle Tertiary
Stratigraphic Age:51.5 Ma - 24 Ma
Minfile ID:092O 053
The Blackdome property is underlain by a sequence of Early- Middle Tertiary volcanic rocks and associated volcaniclastic sediments cut by small intermediate to mafic dykes. Age dates obtained on the volcanic sequence range between 51.5 Ma from dacite to 24 Ma from plateau basalt (Exploration in British Columbia 1986). The rocks strike north-northeast with shallow, 10-20 degree dips to the southeast. Tension fractures are the locus of epithermal precious metal-bearing veins. These fractures have apparently been produced by doming. Minor normal faulting effects dislocations of some units and preserves some of the erosional remnants from younger rocks.
Miocene, fine-grained, porphyritic, dark brown to black basalt flows cap Black Dome Mountain and are the youngest rocks. Basaltic feeder dykes are present across the property. Underlying the basalt is a uniform, 150-metre thick sequence of porphyritic andesite flows. When unaltered, they are green-grey in colour with white plagioclase phenocrysts. Again, numerous feeder dykes for the andesite have been identified on the property. A thin, irregular and discontinuous clastic unit underlies the porphyritic andesite. The clastic unit varies from volcaniclastic sandstone to coarse agglomerate with mafic bombs up to 40 centimetres long. This unit can be 30 metres thick but mostly occurs as small, local erosional remnants. To the south, a chaotic "rhyolite" unit underlies the porphyritic andesite. This unit is actually a mixture of rhyolitic flows, tuffs and breccias as well as local lenses of volcanic wacke and ash beds. The unit is 60 metres thick and thickens to the south. Underlying the "rhyolite" and beneath the clastic horizon at the base of the andesite unit north and northeast of the "rhyolite", are a series of porphyritic dacite flows. They are typically fine-grained, dense, reddish brown to green-grey with 20 per cent white feldspar phenocrysts. This unit is up to 75 metres thick. Andesitic flows with propylitic alteration, tuffs and agglomerate underlie the dacite unit. These andesites are light to dark green with various amounts of chlorite and frequent stringers of epidote and calcite. This is the oldest unit on the property and may be over 180 metres thick.
The metamorphic facies of the volcanics is predominantly zeolite facies with possible lower greenschist facies implications.
Mineralized quartz veins have been found over an area measuring 4500 by 1500 metres at the Blackdome property and are part of an intense fracture system within the Tertiary volcanics. Two persistent vein systems, the No. 1 and No. 2, parallel the southwest spur of Black Dome Mountain and coalesce to the south. It is within the No. 1 and 2 vein systems that most of the production and reserves have been documented. A total of twelve quartz veins have been identified. Some vein names are Giant, Red Bird, No. 17, No. 18, Skiber, Ridge, Dawson and Watson. Veins have been traced over a strike length in excess of 2500 metres with widths averaging 1.5 to 2 metres.
The quartz vein systems are hosted by andesites and rhyolitic rocks which exhibit pervasive potassium metasomatism and propylitic alteration, with the development of a replacement association of epidote (variety pistacite) -chlorite-carbonate-adularia. The propylitic alteration appears to be a broader scale feature and is not limited to those areas invaded by metalliferous veins. The rocks of the rhyolitic unit also frequently exhibit strong, localized argillic alteration represented by montmorillonite and illite. The argillic alteration is not confined to the spatial extent of the ore zones. The ore veins are characterized by a distinct alteration halo which can extend 1-15 metres beyond the veins. The alteration is characterized by noticeable bleaching of the propylitized host volcanics and by the development of a replacive assemblage of quartz-adularia-sericite, including illite/smectite-montmorillonite- kaolinite, minor carbonate and minor chlorite.
The No. 1 vein system appears to have been formed by the infilling of dilatant tensional fractures by quartz, adularia, carbonate, sulphides and numerous other hydrothermal minerals. The infilling of these tensional fractures took place in three separate stages, namely: the pre-ore stage, the ore stage, and the post-ore stage. The pre-ore stage signature is typified by quartz and sulphide minerals deposited on the vein walls. The ore stage is dominated by the deposition of quartz, adularia, and numerous other minor silicate phases, along with sulphide and precious metal minerals. During the post-ore stage, quartz, carbonate, zeolites and other hydrothermal minerals dominated as fracture-infillings, overgrowths and minor open-space fillings. The vein mineralogy may be broken down into four major categories - gangue minerals; gold-bearing minerals, including native gold; silver-bearing minerals, including native silver; and non-precious metal minerals.
Quartz is the most abundant and dominant gangue mineral in all stages of the Blackdome veins. In the pre-ore stage, quartz appears as massive crystalline quartz, lining veinlets and vein walls. It also occurs as euhedral, cockscomb quartz with clear to milky crystals up to a maximum of 10 centimetres length. Crustifications due to impurities and sulphides, are noted along the vein walls. Quartz deposited during the ore stage is predominantly a mosaic of massive milky and grey material commonly intergrown with adularia and minor carbonate and sulphides but may also be of euhedral form. The post-ore stage quartz appears as overgrowths and as vein infillings. Adularia is a major gangue phase of the ore and post-ore stages. In the ore stage, adularia is almost as common as quartz in some sections. It occurs as anhedral mosaics intergrown with quartz, as replacement textures in altered host and primarily as micro-veinlets within brecciated fragments in the fault zone. In the post-ore stage, adularia is much less abundant than in the ore-stage, and occurs as fracture infillings. Carbonate (identified as calcite) is a minor component in the ore stage. It occurs primarily as anhedral mosaics intergrown with the quartz and adularia. In the post-ore stage, calcite occurs as a major component and appears as anhedral mosaics intergrown with quartz and adularia. The clay minerals observed within the ore zone vary from being major to minor components of the vein-fill material. Pre-ore stage clay material consists of montmorillonite, mixed-layer illite/smectite and minor kaolinite. The ore stage is dominated by abundant illite, lesser amounts of mixed-layer illite/smectite and minor kaolinite. The post-ore stage clay minerals are dominated by illite. Chlorite occurs as trace amounts as a vein-fill material.
Ore mineralogy comprises native gold, electrum, acanthite, acanthite-aguilarite, native silver and silver sulphosalts. Native gold occurs as minute, isolated grains of different sizes in tiny veinlets of pyrite and primarily within acanthite-aguilarite grains. Gold also occurs as free gold in vugs and appears to be closely associated with illite and illite-smectite mixed-layer clays. Electrum (25 per cent or greater silver) is more common than native gold. It occurs within quartz, between quartz and adularia grains, within tiny veinlets cutting pyrite and chalcopyrite, as well as within the acanthite-aguilarite grains and masses. It is common to see electrum replacing silver sulphosalts and silver minerals. Acanthite may be the most important silver mineral along with minerals of the acanthite-aguilarite series. It commonly occurs as abundant fine-grained disseminations in the veins and veinlets of quartz-adularia-carbonate and clay minerals. It also occurs as inclusions in pyrite, associated with chalcopyrite, galena and sphalerite. The acanthite can contain up to 4.7 per cent selenium before it is referred to as acanthite-aguilarite. The acanthite- aguilarite series has the same appearance as acanthite and is the second most abundant silver mineral. It also occurs as fine-grained disseminated material. Native silver is interpreted to be present in acanthite and acanthite-aguilarite grains containing very high silver (up to 88 per cent). Microprobe analyses strongly suggest that native silver may be a mineral phase intergrown with the acanthite- aguilarite composition. Microprobe analyses has also determined that a greenish-grey material, included within inclusions of chalcopyrite and galena in pyrite, is a sulphosalt mineral such as tennanite-tetrahedrite, polybasite or stephanite.
Sulphide minerals within the vein systems includes pyrite, chalcopyrite, galena, sphalerite, marcasite, pyrrhotite, arsenopyrite, bornite, digenite, covellite and pyrolusite. The most abundant sulphide mineral in the No. 1 vein system is pyrite. It occurs primarily as minute disseminated cubes up to 1 millimetre across, intergrown with pre-ore stage quartz and as disseminated grains and veinlets, or is contained in masses associated with ore-stage quartz. In post-ore stage material, pyrite is generally disseminated and often shows alteration to goethite and limonite. The second most abundant sulphide is chalcopyrite and commonly occurs as anhedral grains and aggregates. It apparently is an exsolution phase in inclusions within pyrite. The chalcopyrite is commonly associated with the silver sulphide minerals in the pyrite. Galena occurs as trace amounts in the veins and commonly occurs with chalcopyrite, sphalerite and silver sulphides as exsolution(?) phases within inclusions of pyrite. Sphalerite occurs in lower concentrations than galena and are found as inclusions, exsolution phases within pyrite, and associated with chalcopyrite, galena and silver sulphides. Marcasite occurs in trace amounts along with pyrrhotite and arsenopyrite. Bornite, digenite and covellite also occur, but in very minor amounts. Pyrolusite occurs as fine-grained anhedral crystals associated with Fe-hydroxides and clay minerals within the vein zone.
Three idealized stages of vein formation have been outlined by mineralogy and morphology. The pre-ore stage involved initial fracturing, cataclasis and brecciation of the volcanic host rocks. Deposition of pre-ore material was slow in that the fault system was inactive for an extended period of time and the crystals grew relatively undisturbed into dilatant fractures. Potassium metasomatism is also a primary feature of the pre-ore stage. Mineralogy associated with pre-ore stage comprises quartz and adularia along with minor calcite, pyrite, clay minerals and possibly acanthite. The ore stage was characterized by the continuation of open-space filling of the vein zone by quartz, adularia, increased calcite and pyrite, along with the silver sulphosalts, acanthite, acanthite-aguilarite, electrum, gold and minor base metals. The clay minerals illite/smectite, illite and kaolinite were prominent during the ore stage as was the brecciation of host fragments, within the vein, and pre-ore breccias. The post-ore stage was dominated by the open-space filling of quartz with minor calcite and adularia. Minor copper, gold and silver mineralization occurred during the post-ore event along with the deposition of pyrite/marcasite. The post-ore clay minerals, illite and chlorite are a very minor component. It appears that all depositional stages were probably initiated by a period of volcanism but the pre-ore and ore stages most likely represent one long depositional sequence. The post-ore stage was likely deposited at a later time, after some hiatus (Vivian 1988).
The Eocene deposits of the Blackdome epithermal field were generated when Tertiary meteoric groundwaters penetrated tensional fracture systems in a cooling, calc-alkalic, emergent island-arc environment. This resultant geothermal field was most likely underlain by a recirculating plume of brine which encountered meteoric waters at paleodepths of 0.5-1.1 kilometres. The precipitation of a wide range of elements leached by the hydrothermal fluids occurred deep within the cooling volcanic edifice. This precipitation was accompanied by extreme local phyllosilicate plus potassium metasomatism and silicification of the walls of the geothermal reservoir. The metalliferous phases were most likely precipitated during episodic boiling of the fluids. The Blackdome deposits belong to the adularia-sericite-type group of volcanic- hosted epithermal precious metal deposits (Vivian, 1988).
Exploration and development of a new vein, named the No. 18, has resulted in inferred reserves of 28,120 tonnes grading 24.68 grams per tonne gold. Of the inferred reserves are measured geological reserves (proven) of 8662 tonnes grading 26.05 grams per tonne gold and 157.68 grams per tonne silver, and indicated reserves of 6485 tonnes grading 26.73 grams per tonne gold and 164.54 grams per tonne silver, all based on a 1.8 metre mining width. Indicated reserves of 62,590 tonnes grading 16.79 grams per tonne gold and 74.04 grams per tonne silver were reported for the rest of the mine in 1989 (Northern Miner, June 18, 1990).
Since the start of production in April 1986, until the end of July 1990, the underground mine had processed a total of 305,614 tonnes of ore which yielded 6303 kilograms of gold and 19,518 kilograms of silver (Northern Miner, August 20, 1990). Mining operations ceased in November 1990 and the last ore was milled in January 1991. In 1990, Blackdome Mining Corp. was the operator of the mine.
Prior to 1994, an independent study indicated a possible 70,800 tonnes grading 14.1 grams per tonne gold (Information Circular 1996-1, page 19).
In 1996, Claimstaker Resources Ltd. and partner Petro Plus Ltd. conducted a program of trenching, drilling and underground drifting and raising in search of new reserves on veins identified in previous work. Encouraging results have been reported. A recent study by the company has outlined a resource of 159,600 tonnes grading 16.11 grams per tonne gold and 37.0 grams per tonne silver (Information Circular 1997-1, page 22).
As of May 1, 1997 ore reserves stood at 155,933 tonnes grading 14.8 grams per tonne gold and 37 grams per tonne silver (T. Schroeter, personal communication, 1997).
A recent mineral inventory study has increased the fully diluted resources to 209,077 tonnes of 14.9 grams per tonne gold and 42.3 grams per tonne silver. Of this resource, a reserve of 177,000 tonnes at 17.6 grams per tonne gold and 49.8 grams per tonne silver is mineable from existing workings (GCNL #244, (Dec.19), 1997).
Claimstaker Resources reopened the mine on October 10, 1998. Reserves at startup were stated as 128 627 tonnes grading 14.0 grams per tonne gold in the proven and probable categories. The total, fully-diluted resource, including drill-indicated resources, is 237 881 tonnes grading 13.1 grams per tonne gold and 37.1 grams per tonne silver (Exploration in BC 1998, page 60 [Claimstaker Resources Ltd., May 27, 1998]).
Claimstaker Resources holds 65 per cent and Jipangu Inc. of Tokyo holds 35 per cent of the mine. The mine shut down on May 14, 1999.
In early 1999, Claimstaker Resources drilled seven holes totaling 1060 metres targeting the No. 11 vein. Claimstaker Resources changed its name to J-Pacific Gold Inc. in September 2001.
The Blackdome property is held 100 per cent by No. 75 Corporate Ventures Ltd., owned equally by J-Pacific Gold Inc. (50 per cent) and Jipangu Inc. (50 per cent). In 1999, drill inferred resources were 124 120 tonnes, averaging 12.8 grams of gold per tonne and 33.7 grams of silver per tonne (J-Pacific Gold Inc. website, March 2002).
In 2001, J-Pacific Gold Inc. completed a program of mine dump sampling at the Blackdome mine.
J-Pacific Gold Inc. acquired 100 per cent ownership in early 2002.
In 2002, J-Pacific Gold Inc. carried out a drilling and sampling program on the Blackdome tailings pond. The tailings gold content had a weighted average of 1.89 grams per tonne over all samples (Assessment Report 26867).
In 2006, J-Pacific Gold Inc. conducted an aerial photograph survey of the area around the Blackdome mine. J-Pacific Gold Inc. also completed a 10-hole drill program that totaled 2014.9 metres depth. These holes were concentrated into the No. 1 and No. 2 veins which have similar mineralization content to the previously mined ore at the Blackdome mine. Highlights of this drill program include drillhole B06-03A, which had values of 14.2 grams per tonne gold and 67.1 grams per tonne silver over 1.9 metres, and drillhole B06-05, which had values of 28.9 grams per tonne gold and 516 grams per tonne silver over 0.3 metres (Assessment Report 29343).
In 2007 J-Pacific Gold Inc. completed a 13-hole drill program with a total depth of 2079.3 metres. Ten of the drillholes targeted vein No. 17, with nine of the 10 holes producing at least 1 gram per tonne gold. Drillhole B07-15 is the most notable with 31.26 grams per tonne gold and 148.1 grams per tonne silver over 0.3 metres inside of a larger interval of 1.8 metres that contained an average of 5.73 grams per tonne gold and 33.3 grams per tonne silver. Drillhole B07-18 was used to test the No. 4 vein, and returned 1.42 grams per tonne gold over 1.2 metres. Four drillholes targeted veins No. 1 and No. 2; however, testing of this target did not return any assays over 1 gram per tonne gold (Assessment Report 30071).
In January 2010, J-Pacific Gold Inc. changed its name to Sona Resources Corp. and in May 2010 reported updated resource estimates for the Blackdome property. Reported indicated resources were 144 500 tonnes grading 11.29 grams per tonne gold and 50.01 grams per tonne silver. Reported inferred resources were 90 600 tonnes grading 8.79 grams per tonne gold and 18.61 grams per tonne silver (Press Release, Sona Resources Corp., May 4, 2010).
In 2013, Sona Resources Corp. signed a memorandum of understanding (MoU) with China Machinery Engineering Corp. (CMEC) to gain financial aid to bring the Blackdome mine and mill back into production, running at a rate of 200 tonnes per day, with feed from Blackdome mine and later, feed trucked from the Elizabeth gold deposit (MINFILE 092O 012), 30 kilometres south of Blackdome.