New Brunswick offers variety of gold environments

The recent grassroots discovery of intrusion-related gold occurrences in the southwestern area of the province highlights the potential for economic precious metal deposits in New Brunswick. Coupled with the recent breakout in gold bullion prices, there hasn’t been a better time to be banging on rocks in this underexplored province.

Gold mineralization has been documented by provincial government geologists in nearly all the main tectonostratigraphic zones of the province in units ranging in age from Neoproterozoic to Carboniferous.

“I find gold showings in the streams everywhere, from the Sussex area clear into Charlotte County,” says Emilio Doiron, a local prospector who heads privately owned Pro-Max Resources.

Many of the occurrences are either directly or indirectly related to magmatism in plutonic and volcanic environments. Some are strictly structurally controlled, and others are associated with volcanic-hosted massive sulphide deposits.

Owing to the complexity of arc and continental plate interactions during Ordovician through Devonian time, a variety of gold depositional environments exist in New Brunswick, including intrusion-related and structurally related styles of mineralization.

In southwestern regions of the province, intermediate-to-felsic intrusions of Lower Devonian age have produced contact metasomatic and porphyry mineralization, and are considered by provincial geologists to be the likely source rocks for numerous, mesothermal, quartz-carbonate vein systems. Some of these systems may represent eroded high-sulphidation epithermal-type deposits.

In the province’s central and northeastern regions, gold in similar environments is associated with Ordovician and Silurian-Devonian felsic-to-mafic intrusions.

Structurally related systems are found near terrane boundaries in steeply dipping fault and shear structures, which formed during the collision of the Avalonian and North American continental plates. The continent-to-continent collision event was also responsible for introducing tin- and tungsten-bearing granites and associated gold occurrences into the Mount Pleasant area during Devonian times.

Equally important is the fact that structurally related gold occurrences formed in high-level, fold-thrust belts in Late Carboniferous to Early Permian time in response to the juxtaposition of the African Craton and the Avalon terrane.

Gold occurrences associated with deep subaqueous exhalative sulphides are restricted to northeastern regions of New Brunswick.

Several other types of gold environments occur in the southern part of the province. Auriferous, intrusion-related hydrothermal breccias and sulphide-rich lodes are associated with Late Devonian, high-silica granite. Paleoplacers and possible sub-areal geothermal systems (low-sulphidation?) are associated with Carboniferous fluvial sedimentary sequences. Gold enrichment has been recorded in peat bogs overlying these Carboniferous rocks.

Freewest Resources Canada (FWR-V) is leading the exploration of promising gold occurrences intimately associated with the Lower Devonian and Ordovician intrusions in the southwestern and central regions of the province. Last year, Freewest discovered a new style of high-grade gold mineralization in the Anomaly A area, some 3 km from the original showings at its Clarence Stream project. Malcolm McLeod, southern regional provincial geologist with the Geological Surveys Branch, says it is a highly significant discovery that increases the potential of the area.

Different setting

“These new gold occurrences exhibit some characteristic of distal intrusion-related deposits, based on the mineral assemblages,” he explains. “It’s a different tectonic setting.”

The original showings were restricted to Silurian stratigraphy, while the new discoveries are well out in the St. Croix belt, an Ordovician-age package.

“The whole area becomes prospective, not just next door to the intrusive,” McLeod adds.

There is evidence of gold-bearing mineralization elsewhere in southern New Brunswick in a different suite of rocks around the formerly producing Lake George antimony mine and the associated Pokiok batholith, and Poplar Mountain. “We have quite a range of known gold deposits related to intrusive activity in New Brunswick,” says McLeod.

The source granites are a particular suite within the St. George and Pokiok batholiths that are 395-410 million years old. These distinct granites are not highly evolved; they are metaluminous and, locally, have abundant metasedimentary xenoliths. A lot of the contamination is likely derived from the Ordovician rocks, which are anomalous in a lot of metals.

McLeod believes these “wet” granites, which are not high-level, incorporated a lot of the county rock material on their ascent, and, as a result of melting or assimilation, they have a lot of metals in the system. With cooling, the elements, particularly gold, were concentrated in the residual fluids, which made their way into fractures and pre-existing regional structures. “That’s quite evident in the Main zone at Clarence Stream,” says McLeod.

Three suites

This suite of granite stands in contrast to the younger series of 365-to-370-million-year-old “dry” tin-tungsten granites, found nearby at Mount Pleasant. Although there has been some gold found in the younger systems, it has been low-grade. With three main suites of granite comprising the St. George batholith, the challenge has been to discern between the mineralizing systems.

A joint federal-provincial Targeted Geoscience Initiative (TGI) project has spent the past couple of years investigating, in detail, the gold occurrences and deposits in the southern New Brunswick region in an effort to develop unified models for their formation and thus provide exploration guidelines for the mining sector.

These goals have been largely met, says McLeod. “We can now fairly confidently say which granites we should be looking at, and we’re getting close to being able to discern their geophysical signatures.” The project was a co-operative effort among government, university and the private sector.

There is also some significant work being finished up on stream-sediment sampling, which, like the tills, is critical to the discovery of additional mineralized zones in the southern part of the province. Geochemical sampling was instrumental in locating the Clarence Stream deposit, as well as the Golden Ridge gold prospect in the Poplar Mountain area. Recent provincial government till sampling northeast of Poplar Mountain has uncovered a couple of “whopping” gold anomalies that sit a couple of kilometres down-ice from the Woodstock fault.

In terms of prospective areas for gold, McLeod says there is still lots of room to work in the Clarence Stream area. He also likes the exploration potential the contact aureole of the Pokiok batholith holds for both gold and antimony. Significant gold is known to exist at the Lake George antimony mine and around the Pokiok batholith.

Poplar Mountain

Wide open is the Poplar Mountain area, where Freewest has demonstrated the potential for large gold-bearing systems, related to a dacitic intrusion along the major regional Woodstock fault.

In the Burnt Hill area of central New Brunswick, the Geological Survey of Canada (GSC) carried out a regional stream-sediment sampling survey in 2002, and results showed anomalous gold values. There are three of four granitic intrusions in the area, which are older but compositionally identical to the Mount Pleasant intrusions. The Burnt Hill granites are tin-tungsten-bearing, and some of the intrusions have a distinctive signature for gold.

Aside from the Murray Brook gossan cap NovaGold Resources mined in the early 1990s, the Bathurst camp hosts several known gold occurrences, including the Elmtree deposit. There is also the potential for structurally related deposits in an accretionary wedge developed above a Silurian subduction zone west of Bathurst. The extreme northern part of the province also holds potential for Carlin-type deposits in the Matapedia belt, where
several occurrences have been documented.

The extensive Carboniferous sedimentary basins in southeastern and south-central New Brunswick offer the potential for hot-springs activity, which really hasn’t been looked at in detail. “We have all the right ingredients in some of our carboniferous rock,” says McLeod. “There are some barite occurrences, which have anomalous gold associated with them, along with jasper veining in the Windsor Formation and overlying rocks.”

Fold-thrust belt

In the Neoproterozoic Avalon terrane of the extreme south (rocks that are the equivalent of Newfoundland’s Avalon Peninsula), Emilio Doiron is investigating several high-grade occurrences associated with a fold-thrust belt in the Cape Spencer area, south of Saint John. The fold-thrust belt is related to the collision of the Meguma against the southern margin of the Avalon. “There is a lot of ground northeast of the past-producing Cape Spencer mine that is prospective,” says McLeod. “There are a lot of drill-ready targets based on previous work and on the work Emilio is doing.”

Gordex Minerals started up the Cape Spencer mine in 1986 as a small vat-leach operation, based on open-pit reserve of 550,000 tonnes grading 2.5 grams gold per tonne, or 44,000 oz. However, the operation never really got off the ground, as Gordex was beset by financial problems from day one. A further 272,000 tonnes grading about 8.5 grams, equivalent to 75,000 oz., were previously drilled-off in the Northeast zone. The mineral rights to the property are now held by Doiron, who has uncovered quartz vein and hematite material, away from the mine site, running as high as 139 grams gold in grab samples. A further 6 km away, hand-trenching on Doiron’s Gold Brook property has yielded 7 grams across 3 metres.

Doiron was also involved with the discovery of a high-grade gold showing in the Marrtown area, north of Sussex. The showing, which was recently drilled by Pathfinder Resources, occurs in the Annidale belt of Ordovician rocks. The Annidale belt hosts several known occurrences, including the Devil Pike Brook, a small high-grade prospect containing 25,000 tons of material grading about half an ounce per tonne. The gold along the belt is related to quartz-carbonate veins in major northeast-striking terrane bounding faults and secondary northwest-trending faults and shear zones.

“The potential for gold in New Brunswick is endless,” says Doiron. There is little doubt that a major gold district containing diverse styles of mineralization is emerging in this underexplored Maritime province.