Northern Lights claims, Troitsa Peak, Whitesail Range, Omineca Mining Division, British Columbia, Canadai

Regional Level Types
Northern Lights claims	Group of Claims
Troitsa Peak	- not defined -
Whitesail Range	Mountain Range
Omineca Mining Division	Mining Division
British Columbia	Province
Canada	Country

The Northern Lights opal claims are located well above the tree- line on the eastern spur of the Troitsa Peak, south of Slide Creek.

The precious and common opal showings on the Northern Lights claims are hosted by Ootsa Lake Group volcanics. These volcanics are well-layered, coarsely plagioclase- and pyroxene-phyric andesite flows, approximately 130 to 200 metres thick, that conformably overlie flows of rhyodacitic composition. The andesite flows are characterized by abundant plagioclase and pyroxene phenocrysts. In the area of the opal occurrences the andesite flows are subhorizontal and sheet-like, each of which range from 1 to about ten metres thick. These flows resemble near-source compound lavas, consisting of a number of relatively thin lens-shaped flows separated by poorly sorted, debris flow deposits. Individual flows are typically massive at their base and grade upwards into oxidized and strongly vesicular tops (over 50 per cent vesicles in the uppermost 20-40 cm). Vesicles are scarce in the center of the larger flows, but in some thinner flows the vesicular texture may persist throughout. Vesicles are filled with a variety of minerals that generally include a combination of chalcedonic quartz, celadonite, zeolites, and carbonates. Chabazite may occur locally.


The dominant opal-bearing lithologies in the area are the debris flows. Less abundant opal-bearing lithologies are massive lava flows and associated flow top breccias and minor, possibly water lain, ashfall tuffs. Massive flows are commonly dark green and mostly porphyritic, although aphyric flows were also observed. The phenocrysts are predominantly plagioclase (up to 2 cm) and pyroxene (<6 mm). Most of the flows are either strongly vesicular or amygdaloidal. The debris flows consist of subangular to subrounded, vesicular, amygdaloidal or massive clasts that typically vary in size from 2 to 100 centimetres, but some may be several metres in size. The flows are matrix- or clastsupported. Some of the debris flows are polymictic, others are oligomictic. The colour of the clasts varies from dark green, brown, and beige to deep brick-red, a feature that is probably related to the degree of oxidation, and possibly permeability. The scoraceous clasts appear most oxidized. The colour of the matrix varies from yellow to red to gray. Reworking of the debris flows is common, as seen by the rounded heterolithic clasts making up the flows. Some of the flows are truncated by thin bedded, possibly waterlain tuffs, but more commonly by younger debris flows. In thin section most of the opal-bearing rocks consist of 10 to 30 per cent plagioclase phenocrysts (up to 15 millimetres in length), amphiboles (0-2%), pyroxene (<2%), opaque oxides (<2%), apatite and opaques (trace). Vesicles may account for more than 20 volume per cent of some rocks. The vesicles may be partially or completely filled by common and precious opal or agate and coated by celadonite or zeolites.

The opal occurrences are located near the brim of a flat-topped ridge within an area 1200 by 2000 metres. There are at least 10 precious opal occurrences. Most of the precious opal extracted for testing purposes by the prospectors was from the Zona Rosa and Ptarmigan occurrences.

In general, opal and agate occur most commonly as open space fillings in the matrix and vesicles of clasts and rarely as thin films along fractures in debris flows and flow top breccias. It occurs also as amygdules in massive flows. Due to the complex history of some of the reworked flows, agate may be present only in the vesicles of individual clasts. In such flows only one clast out of fifty may contain agate fillings. Geopetal indicators generally suggest that the agate and opal formed when the lithological units acquired their present orientation. However, in rare cases they suggest that the strata has been tilted approximately 15 degrees south since the agate was formed. Celadonite, a soft, green, earthy mineral of the mica group, is present throughout the area as a vesicle filling and in some places it is so abundant that it gives the rocks a bright green colour. Celadonite commonly forms the rims of empty or agate filled vesicules, suggesting that celadonite predated agate.

Two of the metre-scale clasts within the same debris flow at the Agate Alley showing, display concentric layering (zoning) in terms of the vesicle fillings. The vesicles within the core zone (central portion) of these clasts are empty (silica-free). The core is surrounded by 10 to 15 centimetres thick zone containing individual vesicles coated by a one millimetre thick celadonite layer. This is in turn surrounded by an outer zone characterized by agate partially or completely filling the vesicles, suggesting that the fluids that deposited the celadonite and agate were penetrating the clast from the more porous matrix and moving inward. The high concentrations of celadonite on the property do not appear to coincide geographically with the high opal concentrations. As at the Klinker deposit, the presence of zeolites within the area indicates a favorable geological environment for opal preservation. The opal stability field is similar to that of clinoptillolite and chabasite.

Most of the agate is colorless, gray or white. The largest agate eggs observed at the site measured up to 15 centimetres in longest dimension. The agate deposition may be in layers or it may form from several nucleation sites simultaneously.

Precious opal occurs as irregular zones filling individual vesicles or fractures in some of the common opal and agate-bearing debris and compound flows. The size of the opal-bearing zones is difficult to evaluate, but the best exposed occurrence is Ptarmigan. At this location the opal occurs within a trench at least one metre deep, 2 metres wide and 5 metres in length. It appears genetically unrelated to the degree of oxidation, filling vesicles in both hematized and unoxidized lava flows. In most cases, vesicle fillings result in small flecks of opal being densely distributed throughout the rock, similar to examples of Honduran opal. Where the vesicles are large, solid opal recovery is possible. In places, the host volcanic material appears fresh and hard, and will probably take a good polish if polished simultaneously with the matrix opal. In other areas it appears porous and soft and may not give adequate support for the opal during processing. Uncommonly thin (<1mm) fractures filled by precious opal have also been observed. Some of these appear suitable for production of assembled stones as doublets and triplets.

The typical precious opal body colours observed at the sites are white, brown and honey yellow, although black is present but scarce. Most of the opal is opaque to translucent (semi-crystal). The play of colours within the precious opal are green, red, blue and yellow (no systematic study was attempted). The stones appear average or better than average in terms of brightness, although, the detailed evaluation is typically done on individual stones and it will commonly vary within a deposit. In general, the bright play of colour remained after the samples were extracted. The brightness of the samples from the "Bright Lights" locality appears strongly enhanced in humid or wet environments. The opal from this occurrence is probably hydrophane, a variety of common opal with a change in opacity and indirectly, intensity of colour, with a corresponding change in water content. Under transmitted light the precious opal typically appears cloudy brownish or greenish in the central portions of the vesicles and it may contain some dehydration. It appears isotropic under polarized light.

Based upon field observations, most of the stones extracted by the prospectors in 1998 may be described as matrix opal of specimen or gem quality. Some of the opal may be suitable for doublets and triplets. Material suitable for iusolid opalli cabochon-making is relatively rare. The stability of the opal from the Northern Lights claim remains to be assessed. Some of the opal is hydrophane, however, the owners of the claims indicate that precious opal cut two or three years ago did not craze (disintegrate) or undergo other undesirable changes. Test marketing of the precious opal jewelry from this deposit is in progress and several artists are determining if the opal is suitable for carving purposes

Other Regions, Features and Areas containing this locality

References