An unusual diamond occurrence near Wawa in northern Ontario is attracting the attention of
A package of unassuming Archean alkaline metavolcanic rocks is yielding significant counts of microdiamonds, bearing little resemblance to the lamprophyre-type dykes that first attracted diamond interest in the area in the mid-1990s. The newly recognized diamond-bearing rocks are exposed on the GQ property of
Kennecott, the Canadian exploration division of
Band-Ore acquired the GQ property in early 2000 based on an initial diamond-bearing find made by local prospectors Terry Nicholson, Michael Tremblay and Jack Robert along a new logging road. The purchase price was $1.2 million, payable over three years, plus 2 million shares.
The prospectors originally sampled two surface showings separated by a distance of 500 metres. The samples were tested for microdiamonds at Kennecott’s caustic fusion laboratory in Thunder Bay. One sample, weighing 63.4 kg, returned 35 micros and 10 macros, including one stone which measured 1.01 mm in its longest dimension. (A macro is defined here as exceeding 0.5 mm in at least one dimension.) The second, 70.5-kg sample yielded nine micros.
Due diligence sampling by Band-Ore confirmed the prospector’s results. A 54.6-kg duplicate sample from the first site yielded 98 micros. Band-Ore tested the area of the original discovery in the spring of 2000, intersecting the diamond-bearing zone in three short holes. Results suggested an erratic diamond distribution in the zone.
Over the course of 2000 and 2001, Band-Ore discovered extensive outcrop exposures of diamond-bearing “heterolithic breccia.” These showings, which numbered in the hundreds, were extensively sampled, revealing 30 different diamond occurrences across the GQ property. These were divided into six major groups or areas.
In a report, consulting geologist Edward Walker says Band-Ore’s work demonstrated that a suite of rocks different from the original diamond discoveries contained larger and more diamonds per kilogram than previously reported in the area.
One of these areas, dubbed the Engagement zone, yielded phenomenally high micro counts. “This different suite of rocks was readily distinguished from the other rock types based on the presence of mica phenocrysts, absence of pargasitic amphibole, size and variety of fragments, and field textures [all of which] suggested these rocks may be extrusive,” states Walker.
A total of 406 kg of outcrop and frost-heaved material collected by Band-Ore from a dozen or so sites across the zone yielded more than 12,000 micros and 340 macros. The best sample, weighing only 24 kg, returned a staggering 2,128 micros and 116 macros, including seven stones exceeding 1 mm in one dimension. Fifty-two of the diamonds measured greater than 0.5 mm in two dimensions. Mechanical stripping indicated the zone was more than 335 metres long with an apparent width of 75 metres.
The zone’s potential for bigger, commercial-size stones was tested in the spring of 2001. A 12.5-tonne mini-bulk sample processed by the Saskatchewan Research Council returned a parcel of 30 stones weighing 0.607 carat, for an implied grade of just 4.8 carats per 100 tonnes (0.05 carat per tonne). The largest diamond was a broken, 1-quarter carat, white octahedral measuring 3.74 by 3.3 by 3.1 mm. The other 29 diamonds were of various colours and ranged in size from 0.7 to 3.06 mm.
Last fall, Kennecott targeted the highly diamondiferous Engagement zone with a program of trenching and channel sampling. Sixty-six channel samples weighing 637 kg were collected from trenched outcrops along a 200-metre strike length. Caustic fusion analysis recovered 6,843 micros and 373 macros, including 33 stones exceeding 0.5 mm in two dimensions. One diamond was greater than 1 mm in two dimensions.
Diamond counts of the 66 samples varied from zero to 998 diamonds per sample. Only one sample had no diamonds.
‘Pyroclastic-Archean’
During a presentation at this year’s Cordilleran Exploration Roundup in Vancouver, B.C., Kennecott geologist Kevin Kivi described the diamond-bearing rocks of the Engagement zone as “pyroclastic, Archean rocks.” The 2.7-billion-year old rocks are part of a suite of alkaline volcanic complexes in the Michipicoten greenstone belt in the Wawa sub-province of the Superior Craton. “They don’t look a lot different from most of the greenstone belts in the Superior Craton,” said Kivi. “It’s only once you get down and sample the rocks that you find out there are diamonds in them.”
The diamond-bearing rocks found at GQ and at Pele’s Festival property are metavolcanic alkaline intrusives and extrusives intercalated with mafic metavolcanic pillow basalts and lava flows of the Catfish assemblage. Intrusive facies of these alkaline rocks are what have been commonly referred to as lamprophyres in the Wawa area. They are characterized as hypabyssal facies and intrusive heterolithic breccias.
The extrusive diamond-bearing rocks, like the Engagement zone, are medium-to-thickly bedded pyroclastic air-fall deposits and debris flows described by Kivi and Edwards as heterolithic tuff-breccias that grade upwards to lapilli-tuff and tuff. The pyroclastics are compositionally similar to the intrusive varieties but with a significantly higher proportion of mica phenocrysts and higher diamond counts.
Both facies contain significant proportions of local country rock fragments. Rare-to-minor deep crustal and mantle rocks, such as banded gneiss and extensively altered talcose ultramafic xenoliths, are present, but fresh mantle rocks, such as lhertzolite, harzburgite and eclogite have not been identified.
Kivi says Kennecott is intrigued by the potential size of these things. The pyroclastic Engagement zone has been mapped for 450 metres of strike length before it disappears under a swamp at one end, and overburden cover at the other end. The zone is exposed 70 metres across strike. “They’re big units,” says Kivi.
Hypabyssal phase
During the fall program, Kennecott also stripped and channel-sampled sections of the Barnett Lake zone, where a diamond-bearing hypabyssal phase outcrops alongside the lake. Trenching exposed a 1,200-sq.-metre section of the unit, with a width exceeding 30 metres. A total of 247 kg in 27 channel samples yielded 207 micro. Diamond counts varied from zero to 19 diamonds per sample, and only one sample contained no diamonds. Previous sampling in the area by Band-Ore yielded 123 micros and three macros from 24 kg of material. Fifty-eight of those diamonds are coloured pink, rose, amber, green and yellow, with the majority of the remainder described as white.
Kennecott plans to carry out soil sampling, geological mapping and drilling.
At the neighbouring Festival property, Pele Mountain has identified 12 diamond occurrences that are grouped into seven areas. According to Edwards, five of these areas exhibit a suite of rocks comparable to a maar-like volcanic complex. Last fall, Pele collected a 100-tonne test sample from the Cristal volcanic complex, which consists of three groupings
of outcrop exposed intermittently over an area of 750 by 400 metres and hosted within pillowed metabasalt, mafic metavolcanics and diorite.
The main Cristal showing occurs near the southern boundary of the property, just 1.5 km north of the Engagement zone. The showing consists of volcanic breccias and clast supported lapilli tuffs overlain by lapilli and ash tuffs that outcrop intermittently over 175 metres. Fifteen grab samples taken across this zone yielded 327 microdiamonds, with ten of the stones greater than 0.5 mm in one dimension. The best results came near the basal section of the lapilli tuff. Three samples, weighing a combined 39.4 kg, returned 159 micros.
96 diamonds
The 100-tonne test sample was collected in the immediate area of these samples from a 10-by-10-metre section. Processed free of charge by De Beers, a 2.31-carat parcel comprising 96 diamonds larger than a 1-mm square-mesh cutoff was recovered, for an implied grade of only 2.13 carats per 100 tonnes (0.02 carat per tonne). The largest diamond recovered weighed just 0.18 carat.
Based on the limited microdiamond sampling of the Cristal showing, together with the macro results, De Beers has modeled a preliminary grade of six carats per 100 tonnes.
Pele followed up by collecting another 10 tonnes from the Cristal showing, 75 metres north of the first, 100-tonne sample. The 10-tonne sample was processed by Lakefield Research, which yielded a 0.25-carat parcel of 49 diamonds measuring greater than 0.5 mm in two dimensions. The largest diamond measured 3.05 by 1.62 by 0.81 mm and weighed only 0.04 carat.
Pele says it has begun preliminary discussions with De Beers exploring possible joint-venture avenues. The South African major is processing an additional 455 kg of sample from the Festival property for microdiamonds.
Other companies active in the Wawa area include
Be the first to comment on "Diamond potential near Wawa lures big guns"