Download Quartz-carbonate

‘It‘ y o u don’t explore, you won’t discover’
In search of the unknown
MCI
coffee ;ind riiuffins nntl n few introductoCraiiston of Natural Rcsources C’;iiinda took the podium nt the 54th
Xliiics mid Energy Ministers’ Confercncc in
St. l o l i n ’ ~Nlld.. and challenged mining cornpanics to pay morc attention to ore types
unknown, or cs5entially unknown. iii Canada.
“Vast ;ireas of our country rcinain only
supcrlici;illy explorcd.” Cranston said. “bccausc riolhing much has evcr been found
there. I h ~ this
t inny be self-fullilling prophesy
- if you don’t explore thcre. you won’t make
discoveries so you won’t explore. Some of
those areas would benefit from more innovative geological mapping and exploration.”
H e said the discoverics of the Voisey’s Bay
deposit illustrate that, until recently, there had
been a lack of exploration in this region of
Labrador.
Going farther back in tinie, exploration
companies have traditionally overlooked the
country’s potential for hosting porphyry copper-type deposits, such as those that exist in
the Western Cordillera, and unconfonnitytypc uranium deposits, such as those that exist
in the Athabasca and Dubawnt Basins
H e also pointed to the discoveries near Lac
cle Gras in the Northwest Territories a. evidence
that there had previously been insufficient
exploration for diamonds in Canada (except for
several low-grade, uneconomic diamondiferous
kifiilxrlites found since the 1960s or 1970s).
Cranston believes Canada‘s huge expanses
o f Archean rocks in Manitoba, Ontario, Quebec and clscwhere are examples of regions
untlerexplored for diamonds
“There must be many other as-yet-unrccognized exploration possibilities in Canada
that can provide additional discoveries to
geologists who apply originality and innovation to thc search for them,” he added.
Cranston has a point. Some of the most
spectacular exploration successes in this counn rcniiirkx Donald
try l q a i i with individuals who went against the
herd mentality and pursued their own goals
Spud 1 iucstis was one such pioneer - a
prospector wlio gaw the value :ind potential
of Dritish Columbia’s low-grade copper
deposits wliicli many others saw as nothing
more tli;in waste rock.
Charles Fipkc found diamonds in a region
of tlic Territories that was once viewed ns so
unprospectivc that government geologists
barely did any mapping in the area.
The Eskay Creek deposit in northwestern
British Columbia is another unusual deposit
type that resulted from good geological detective work and the unflagging determination of Murray Pczim’s exploration team.
fezim also was a trail-blazer in Ontario,
where he financed exploration work o n a
known gold prospect that few thought had
much promiscThe flamboyant promoter didn’t
worry about the naysayers; he backed his geologists until the drills hit the Hemlo motherlode
on the 76th hole.
The Quebec government has been a pioneer in its efforts to stimulate the search for
non-traditional deposits Not only does it provide incentives for companies to pursue this
exploration effort; it lays the foundation by
GEOLOGY 10l/DEREK WILTON
gathering and providing geological data to
support the private sector.
All in all. Cranston believes that, although
exploration and discovery levels in Canada
are healthy, domestic spending is growing
more slowly than spending on international
projects. Still. as the old saying goes we can
not rest on our ores. We need more explo- Quartz-carbonate vein gold deposits (also characterized by abundant, typically iron-rich,
ration leaders: that is, people charting their known as mesothermal lode deposits) form hydrothermal carbonate alteration assemown course and not just following the pack.
along, and are localized to, major regional blages which spread into the host rock from
But. please, no bulk-tonnage, maar-dia- fault and fracture systems, but are actually the vein. They represent pulses of fluid which
treme deposits with “paystreaks” of alluvial located in secondary or tertiary structures flowed along the fracture/fault plane into the
gold and miraculous metallurgy.That produc- These vein deposits form from hydrothermal surrounding country rock with which they are
tion number has already been staged, and (hot aqueous) fluids, which were derived not in chemical equilibrium, producing chemHollywood is making the movie.
deep in the earth’s crust at a medium geolog- ical reactions and the resultant alteration halo.
ical temperature (250 to 400°C).
Alteration associated with gold mineralThe fluids use the faulvfracture zones as ization also involves sulphidation (sulphide
permeable channels along which to flow from halos are a characteristic alteration phenomtheir region of origin until tlicy reach a point enon of most qirnrIz-ci~rfmnnfevein #old
wherein any of a nunibcr of factors -chem- deposits) and potassium m~1ammatbm
ical reactions with country rock andlor (pptassium is usually enriched in the alterchanges in the temperature a n d o r pressure ation halo around the veins). These halos
-causes the fluids to precipitate. Vie gold overprint pre-existing alteration assemblages
precipitates out of solution along with the in the host rock.
Any rock type can host these vein systems,
quartz vein material.These regional fault systems develop during the waning stages of but, at best, they are developed in mafic rocks
continental collision and hence can form at such as basal6 greenstones, gabbros and tursignificantly later periods than the host rocks; biditic shaley sedimentary rocks; this is attributable to the chemical contrasts between host
as such, they are termed “epigenetic.”
The actual host rocks of the quartztar- rock and ore IluidsThe ore fluids are silica-rich
bonate veins are affected by these faultlfrac- with carbon dioxide and potassium; hence they
ture origins and can range from mylonites to react best with malic rocks, which d o not confault gouge. Mylonites indicate deformation tain free silica but which have calcium-ironunder confining pressures sufficiently high magnesium silicates that can react with cirbon
that the rock recrystallizes to a fine grain size. dioxide to form carbonate alteration minerals
Gold abundances are characteristically
This is plastic or ductile behavior, and indicates that the vein formed deep in the earth’s low in most geological m a t e r i a l s n e average
crust. Alternatively, if the faulUfracture cuts a crustal abundance of gold is o n the order of 3
rock at a level close to the earth’s surface, parts per billion, and generally no single rock
then it does not have the same confining pres- type is preferentially enriched in gold.
As a result of the low background contents
sure and hence will break into fault gouge.
Qpical quartz-carbonate vein gold deposits of gold, a large amount of rock must be affectconsist of quartz veins with gold, pyrite and/or ed by the hydrothermal fluids in order for sufarsenopyrite.The gold is usually pure gold and ficient deposits of dissolved gold to be formed.
can be present in textures ranging from soli- The general model for these deposits suggests
tary grains to grains intimately intergrown that the associated regional faults have deep
with sulphide minerals In some deposits gold roots that cxtend down to the lower crust.
is present as “invisible” intergrowths with sul- Hydrothermal fluids, which contain gold disphide minerals such as arsenopyrite (that i s solved from a wide region, are formed, and
the gold is in the crystal lattice of the sulphide these are focused up along the faults to higher
mineral). In other deposits, the gold is not pure levels in the crust, where they react with counbut electrum -a mineral made up of gold, try rock to fonn lode gold ores
The airtlior ir a geology professor at Memwith 20% to 80% silver.
Quartzcarbonate vein gold systems are orial University in St. John$ Nfld..
Quartz-carbonate
vein gold deposits, Part 1
.
are locked,” explained the pit su
when I dled.‘?t’s a tad difficultto move
the order on to our procuremen
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