New data from the Uran-Barry Belt
Pierre Rhéaume and Daniel Bandyayera
Direction de Géologie Québec
During the summer of 2005, Géologie
Québec conducted field studies at selected sites in
the Urban-Barry Belt (UBB), particularly in the Lac Windfall and
Lac Rouleau sectors. Newly stripped zones and recent drill cores
were examined to gain a better understanding of the geological context
of the gold mineralization for which the sector is known. Preliminary
examination of the collected data reveals several similarities between
the Lac Windfall sector and epithermal precious metal deposits.
This work supports previous studies and highlights
the development of several types of auriferous mineralization during
the UBB’s geological history. In particular, the hypothesis
of a large epithermal system in felsic and intermediate rocks for
the Windfall and Rouleau members has significant consequences for
exploration. The following features are considered particularly
- Epithermal-type mineralization observed thus far is associated
with recognizable alteration defined by silicification, carbonatization,
potassium gain, sodium depletion and the presence of tourmaline.
This signature, evident in the field, can serve as an exploration
- The effects of this epithermal system can be seen within a broad
area which includes several rock types. This hydrothermal signature
is notably (but not exclusively) expressed in the Lac Windfall-Lac
Rouleau sector and the Lac aux Loutres sector. The exploration
for epithermal precious metal deposits should take into account
such a large volume of altered rocks.
- The structural style in the UBBfeatures doubly plunging folds
and structural imbrication from south to north which are favourable
to the preservation of extensions of the main altered unitsat
relatively shallow depths.
Location and geological context
The UBB is located 100 km south of Chapais
(Figure 1). It consists dominantly of
volcanic rocks and extends for 135 km from Lac Wilson in the
west to the Grenville Front in the east. The UBB displays a prominent
E-W structural trend marked by doubly plunging folds and E-W faults
that produce thrusting to the north (Figure 2).
Numerous felsic volcanic assemblages are present, including the
Novellet (2,714 Ma), Freeman (2,701 Ma), Windfall (2,718 Ma),
Rouleau, Chanceux (2,727 Ma) and Fecteau (2,791 Ma) members.
Location of the Urban-Barry Belt.
Simplified geology of the Urban-Barry Belt.
The 2005 work focused primarily on the Windfall
and Rouleau members where a number of exploration companies, including
Ressources Murgor Inc., Noront Resources Ltd. and Beaufield Consolidated
Resources Ltd., have been active for several years. Stripping and
drilling in the Windfall sector revealed pyritic stockworks crosscutting
a complex of quartzo-feldspathic porphyry sills, andesites and felsic
tuffs. The stockworks (Figure 3) are
typically only weakly deformed and have yielded gold grades of more
than 10 g/t Au. The Au/Ag ratio for the samples collected
in 2005 is high, on the order of 1/1, and the host rock displays
alteration that is often intense and characterized by silicification,
carbonatization, potassium gain and sodium depletion. Pyrite also
contains tourmaline needles and locally forms tourmaline-cemented
breccia similar to that found in the Lac
aux Loutres sector.
Sample from a gold-bearing interval
displaying a pyritic stockwork in an intensely silicified
zone (drill hole NOT-4-27).
Detail of the boxed area in A displaying brownish tourmaline
crystals with triangular cross-sections in pyrite. Sample
provided by Noront Resources Ltd.
Current information indicates that mineralization
predates deformation and is syn-volcanic in origin. The early timing
of the mineralization, the development of pyrite-gold stockworks
in silicified zones with a potassic alteration halo, and the Au/Ag
ratio of about 1 collectively suggest that these mineralizations
belong to a large epithermal system or to an alteration pipe in
an auriferous volcanogenic-exhalative system.
Considerable quantities of disseminated tourmaline
(1-2%) and pyrite were also observed in intermediate tuffs west
of Lac Rouleau. south of the Windfall sector (NAD 83–18
- 454587E - 5431846N). These tuffs coincide with a folded magnetic
high that can be followed for several kilometres.
The Lac Rouleau sector has very little exposure
and was mainly investigated by studying drill core. Core samples
are currently being processed for lithogeochemical analysis that
will help characterize this large unit. The rocks of the Rouleau
Member observed in drill core were mostly lapilli or block tuffs
of intermediate composition. We also observed significant carbonate
alteration locally associated with shearing, as well as quartz veins
and specks of visible gold. Earlier work reported reserves of 544,000 t
grading 7.2 g/t Au. Preliminary evidence is compatible
with vein-type mesothermal gold mineralization.