Quartz eye feldspar porphyry
Virtual Museum ID: 19-BCGS-BOB88-1
Quartz is the second most abundant mineral on Earth, occurring in many different types of rocks. Although usually clear or milky white in colour, quartz can be found in a variety of colours because of impurities in the crystal structure. Pure quartz is made up of silicon and oxygen only, but atoms of other elements, like iron or titanium, often make their way into the quartz crystal structure. Some varieties of quartz, like purple amethyst, are considered to be semi-precious gemstones and have been used since ancient times to make jewellery and decorative objects.
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-BOB88-1
Date Added to VM:2019-05-07
Sample Origin:Michelle Creek
Specific Site:Bob Claims
Datum:10 (NAD 83)
Primary Features:Quartz eye feldspar porphyry
Primary Mineral Formula:-
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 Formation:Skeena Group
Geological Period:Lower Cretaceous-Lower Tertiary
Stratigraphic Age:145 - 23.03 Ma
Geological Terrane:Overlap Assemblage
Minfile ID:093B 054
The Bob claims are located 10 kilometres south of Nazco, on Michelle Creek. The Bob area has also been claimed under the names Esker, Naz, McKay and PM 1-6.
The region is underlain mainly by sedimentary rocks of Lower Cretaceous and Lower Tertiary ages and overlain by Miocene plateau basalt. Cretaceous rocks consist of conglomerate, sandstone and some interbedded argillite. The Cretaceous sedimentary rocks are considered to be correlative with the Skeena Group sediments which are of similar type and composition. These rocks dip 15 degrees to the southwest and are cut by north-northeast and west-northwest striking fracture systems with steep dips. These rocks locally exhibit variable bedding attitudes, suggesting local post-deposition folding. The sediments generally appear to have good lateral continuity, with local thickening, thinning and lateral facies changes.
The Cretaceous sedimentary rocks are unconformably overlaid by andesite-basalt, basalt breccias and rhyolite breccias of probable Paleocene-Eocene age.The massive basalts and basalt breccias appear to unconformably overlie the Skeena Group rocks along the eastern edge of the property. Whereas the younger andesite-basalt cinder type volcanic rocks locally overlie the Skeena Group rocks along the western side of the property.
Quartz eye-feldspar porphyry dykes and/or sills of probable Tertiary age crosscut the
Skeena Group sedimentary rocks. These dykes appear to strike generally north-south.
Anomalous concentrations of gold and pathfinder elements are associated with silicification and "clay" or argillic alteration within the property area, with lesser amounts of carbonate, feldspar and chlorite. Abundant hematite and limonite within 100 m of the ground surface appear to reflect a deep oxidation profile, and also appear to be associated with anomalous concentrations of gold and the pathfinder elements arsenic, mercury and antimony. The hematite and limonite likely formed after primary (hypogene) pyrite. Pyrite occurs with minor amounts of arsenopyrite, stibnite and galena below about 100 metres depth; pyrite is locally seen higher in the section, nearby the quartz eye-feldspar porphyry dykes. The upper oxidized and altered zone within the sedimentary rocks is also characterized by replacement of feldspars by sericite and "clay".
The Bob group was initially staked by Lac Minerals in 1983 with geochemical surveys being performed the same and following year. In 1985, 19 percussion drillholes (1169.7 metres) were completed. The next year, another thirteen reverse circulation drillholes and four diamond-drill holes were completed on the property. The best result from assayed cores, at this time, returned 1.10 grams per tonne gold over 3.05 metres (Property File Rimfire, 1987). In 1986, a drilling program consisting of twenty holes totalling 3114.9 metres were completed on the property. In 1987, 1685 metres of core drilling and 2983 metres of circulation drillholes were completed. This work was accompanied by an induced polarization survey and a further 559.6 metres of reverse circulation drilling, over 10 holes, in 1988. Grid drilling in 1988 had outlined a mineral inventory of 384,200 tonnes grading 0.75 grams per tonne Au (Property File Rimfire Eighty Eight Resources Ltd., 1990).
The adjoining Naz claim group was staked in 1983 by Lac Minerals to cover a multielement soil geochemical anomaly. Eldor Resources identified a gold and silver anomaly in 1984 and performed a shallow overburden drilling program followed by a VLF-EM survey. In 1985, sampling on the property returned 0.10 per cent Cu over 2 metres (Property File Rimfire Eldor Resources Ltd., 1987). Line cutting and a geochemical survey were performed on the nearby McKay claims in 1987. In 1988, geochemical and induced polarization surveys and three circulation drillholes (228.6 metres) were performed on the nearby Esker claims.
A total of 422.15 m was cored in three holes at the Nechako Gold property between
November 20 and December 2, 2005.