3. 3
Executive Summary
The Prospecting Licence (C-68) located in the Cuyuni Mining District No. 4 as shown on
Terra Surveys Topographic Map 18SW, as shown in fig 10 and enclosing an area of
approximately 10194 acres of the Ekabago River. The potential of the area for gold is
very good.
The PL is presently under mining license by C B & R Mining Enterprises. Active gold
extraction is presently undertaken by land dredging, using excavators on mining concesions
bordering this PL.
The PL area is located in the upper drainage portion of the Ekabago River that drains in
the Puruni River,and close to the mouth of the Waikuri River that drains into the Cuyuni
River, approximately 150 km due west of the city of Georgetown .
Based on information from surface mapping in the areas of the soil geochemical anomalies
suggest the majority of the alluvial gold and gold anomaly areas located to the north/west of
this, see fig 3, PL are likely related to zones of weakly mineralized, structurally deformed,
lithological contact between mafic and felsic volcanic or intrusive rocks which interlayer with
more extensive packages of sedimentary formations. A portion (perhaps the majority) of the
gold mineralization may have been derived from quartz lode type occurrences in
lithologically controlled shear structures.
The geology of the area consists of Lower Proterozoic Mazaruni Supergroup (greenstone
belts) consisting of meta-sediments and meta-volcanic rocks, intruded by Younger Granites.
Unconformably overlying these rocks is the Roraima Formation, a generally flat lying series
of conglomerates, sandstones, shales and with minor interbedded volcanics. All of these
rocks (greenstones, granites, and post-orogenic sedimentary series), are intruded by
doleritic and gabbroic dikes and sills (the Younger Basic Intrusive Suite), see fig 4-6.
4. 4
Location and Access
The PL area can be accessed by 4WD vehicle or Bedford truck via a logging and mining
road from Bartica, crossing the Mazaruni at Itaballi,from Itaballi the journey by truck/pick up
is approximately 5-6 hours to the PL . Bartica is accessed from Georgetown via speed boat
from Parika, or by road via the Georgetown-Linden Highway crossing the Essequibo River
at the Shirima crossing, see fig 1.
Geophysics
The first systematic geophysical survey in Guyana was an aeromagnetic survey flown by
Aero Services Corporation, funded by the United Nations in 1963. The survey used a set of
N-S flight lines at a spacing of approximately 1.6 to 2.4 km, and a height of 300m. In 1971-
72 additional areas in Guyana were flown by Terra Surveys, funded by the Canadian
Commonwealth Bureau, and older data was incorporated in a set of 1:200,000 scale map.
These sheets were then re-issued with an interpretation by Tyl & Reford of Terra Surveys
Ltd in 1973. In 1994 aeromagnetic data covering Guyana was converted to digital form by
Gtech Ltd, a commercial group attached to the University of Leeds in the UK as part of the
“South American Magnetic Mapping Project” (SAMMP). A relief-shaded map compiled
recently (Heesterman 2004) from this data. It should be noted that this data has not been
reduced to the pole.
The aeromagnetic data shows distinct areas with magnetic highs, or abrupt magnetic
gradients,see fig 7. The Quartzstone mountains, which trend north-south, directly to the west
of the study locations (excluding Wiamu) show elevated geophysics results to the immediate
background geophysics. `
5. 5
Mineral Occurrences
Historical Data
Historically the plains underlain by granitic saprolite in the area has been a good source of
gold. However recent sampling from this area has not determined a significant source of
gold in the granitic saprolite, which is now exposed. It is therefore suggested that historical
extraction of gold has derived from alluvial material deposited on the bed rock which has
subsequently been removed and processed for gold. The alluvial material is most likely to be
derived from lode structures and schistose rocks observed and from the hill ranges. It is
therefore seen as an important exercise to study the hill range of the area for primary
mineralization.
The Quartzstone – Aremu Batholith which within the PL area is associated with the
extensive surface gold workings along the contact zone with the country rock. Gold occurs in
the contact zone, marginal granite and gold bearing quartz veins, which are usually
associated with shear zones (Annual Report, 1964)
PL Mineralisation
From data on the mining activities bordering the PL, gold is found to be present in
quartz veins and quartz rich lodes and well foliated saprolitic schist which in general all
strike north-south throughout the area. The gold bearing quartz veins are usually
associated with a black mineral (tourmaline?). Active extraction of gold from saprolite
and quartz material in areas bordering the PL area is presently undertaken by small and
medium scale miner. In some areas saprolite and quartz is being crushed and washed.
One notably anomalous area is located within the PL area with Au assay values up to
212 ppb, see fig 2, however it should be noted that approximately sixty percent (60%) of
the PL area have subjected to geochemical sampling, as shown in fig 2, with no
information on soil sampling. Mineralized quartz was located at two locations within the
PL, as shown in fig 8.Alluvial mineralization and Gold anomaly is located south-eastern
part of the concession and just north east , as shown in fig 3.
6. 6
Regional Geology
Two major lithological sequences, the Bartica Assemblage and the Barama – Mazaruni
Supergroup Greenstone sequences, underlie the northwestern area of Guyana.
Basement – the Kanuku complex is considered to be part of the Archean basement. It
consists of paragneisses and migmatites, granulites (Kanuku Mts.) and granite
gneisses.
Greenstones - The Barama and Mazaruni groups have been classically considered as
part of the Guiana Shield’s widespread Birrimian Age Greenstone Belts (2.2 G.a). The
Barama group outcrops in the northwestern region of Guyana, close to the border with
Venezuela. It consists of a predominantly sedimentary sequence with locally developed
Mn rich chert layers (Mathews Ridge deposit) interbeded with volcano sedimentary
packages. It is bounded to the west by the predominantly volcanic Mazaruni group (El
Callao in Venezuela stratigraphy). The contacts between The Mazaruni group, the
Barama Group and the gneissic basement sequences have not been well defined.
Generalized descriptions by Gibbs and Barron, made at Waikuri, suggest a typical
Archean greenstone sequence, with ultramafics rocks in the lower part, andesitic and
felsic volcanics in the central part and sediments in the upper part. All the above
sequences were deformed during the Trans Amazonian Event (2.1-1.9 Ga.).
Older Basic Rocks – this is a distinct group, also of Birrimian age, and is described as
intruding the Barama –Mazaruni greenstones. These are deformed and
metamorphosed to the same degree as the host sequences (Heesterman 2001).
7. 7
The Bartica assemblage is a gneissic terrain, occurring in the Cuyuni River Region,
composed of various ortho / paragneisses with amphibolites, metamorphosed to the
amphibolite facies. Locally it reached the granulite facies. These rocks are believed
(Gibbs and Barron) to be reworked Barama-Mazaruni units during the Trans Amazonian
event (1.95 to 2.2 Ga). Other authors believe the Bartica assemblage is another
basement portion of Archean age
Of similar age, but clearly late, are the so-called Younger Granites. These are generally
small individual intrusions forming large complexes of granitic terrain. Their composition
varies from granitic to dacitic. Gibbs and Barrow describe the Aurora Complex, as
composed of three rock types: tonalites, granodiorites and leucogranites. They are
unfoliated and display saussuritization (sericite + epidote), and sometimes are sheared
by later events.
The above rocks are intruded by sills and dikes and overlain by flat lying, undeformed
volcanics, probably, of the middle Proterozoic age. These could be related to the 1.8 Ga
Uatuma event, and correlate to the Kuyuwini volcanics, mapped originally in the
southern portion of Guyana.
C-67 Area Geology
Generally, the geology of this area is very similar to that seen in other parts of the
greenstone belts of Guyana, with the oldest rocks consisting of the Mazaruni Supergroup,
as shown in fig 4-6. The local geology is presented in terms of the Landsat interpretation,
geophysical features and limited information from geological mapping in thick laterite terrain
and scarce outcrop exposure along grids lines and riverbeds. Given the scarcity of outcrops,
information is more often derived from mapping float and saprolite. Differential recessive
weathering of soft rocks and positive relief from more resistant (fresher) rock types can
create the false impression of an abundance of the latter units in the field. All sulphides at
surface are readily weathered, except where they are dispersed in competent metacherts or
siliceous volcanic rocks. This differential weathering feature in the presence of sulphides
and/or alteration zones and/or permeable structures, can however locally enhance exposure
via the development of deep erosional cuts at surface.
8. 8
In several areas in Northern Brazil this is noticed and an interesting example is the
Amapari skarn deposit, located in Amapá state. In Guyana the mineralized zone is
deeply weathered to as much as 140m while the adjacent rock units are generally only
weakly weathered and oxidized to depths of 20 to 60 meters.
Greenstone Belts: These areas was identified using Landsat interpretation, the
greenstone sequence is the predominant rock type, and is characterized by a weak, but
persistent, bedding or foliation generally trending NNW-SSE. Because of the weak
contrast in the Landsat imagery of the bedding/foliation, it was not possible to determine
the internal structure of the units or to separate it into predominantly volcanic or
sedimentary units. Only a few resistive ridges were clearly identified and interpreted to
consist of either massive volcanics, sandstones, chert or BIF.
Structure and relative age
A study of lineaments from stereoscopic examination of air photos was modified using
aeromagnetic and field data to identify major structures. Where all different data types
coincide, the probability that the structure is significant is higher. A similar process was used
to define major lithological boundaries.
Historically very few faults have been mapped in the field, mainly as softer faulted material
rarely survives as outcrop. Airphoto interpretation suggests that many linear features can be
traced between photographs over long distances. At least some of these must be faults with
significant movement, and others are first and second order fracture systems related to
primary movement. Some of the larger lineaments thought to be faults and fractures are
shown in Figures 8.
A number of main lineament directions can be recognised. Age relationships of some of
these can be interpreted from the way that they control the geology and mineralisation, but
in many cases these structures may be long lived, and have been re-activated several
times.
9. 9
Comments & Conclusions
Based on the body of data on this concession, further exploration activity which entails
detailed soil and geological mapping is required to accurately define the grade and type
of mineralisation,however from the mining activities that bordering this PL and the
mineralized quartz located within the concession it can be assumed that gold
mineralization is hosted in quartz veins and quartz rich lodes in this PL also. Therefore it
is suggested that further work to better understand the geology in this concession
should be undertaken as there may be a significant source of primary gold.
19. 19
REFERENCES :
Bishop DW. 1936. Quartzstone-Wiamu area. Cuyuni River. Preliminary report
Annual Report of Geological Services Department, British Guiana. 1964. Special
geological problems. Granite studies: Quartzstone – Aremu, Rupa, Kopang. 33-35
Learmont J W. 1954. Area vbetween Aremu and Quartzstone Rivers, Cuyuni Rivers.
Annual Report on the Geological Survey Department for the Year 1954 (British Guiana
Geological Survey). 42-43, 88-89
Lloyd JW. 1958, Area North-west of Quartzstone Landing, Cuyuni River. Annual Report
on the Geological Survey Department for the Year 1958 (British Guiana Geological
Survey). 42-43
