SOME PRELIMINARY RESULTS ON THE
GOLD EXPLORATION PROGRAM OF PU SAM CÁP PROJECT OF TRIPLE PLATE JUNCTION Ltd, VIỆT
NAM
BILL HOWELL, NGUYỄN
THỊ THỤC ANH, MATTHEW FARMER, BÙI XUÂN VINH
Triple Plate Junction Ltd.
Abstract: Triple Plate Junction Ltd is a British
foreign company having a legally registered representative office in Việt
TPJ has the current
legal status to cooperate with Vietnamese partners: Việt Nam National
Minerals Corporation (VIMICO), Lai Châu Minerals Company Limited (LCMC) and
Thăng Long Construction & Investment Development Joint Stock Co
(TLINCOND), previously named as Mountainous Construction and Trading Company
(VIETRACIMEX-MTC).
On 23 March 2005, TPJ
and the Vietnamese Partners were granted Exploration License Nos. 316/GP-BTNMT
and 317/GP-BTNMT by Ministry of Natural Resources and Environment (MNRE) to
conduct exploration for gold in areas Nos. 1 and 2, Pu Sam Cáp Region, Lai Châu
Province.
Although Pu Sam Cáp is the region where there are complicated geological activities and difficult working environment conditions, but by applying many advanced exploration methods and using Vietnamese and foreign consultants and experts, TPJ’s exploration program has been achieved some initial elevated successes. Beside showing clearer geological and mineral features, some unknown gold mineralized zones have been identified in Pu Sam Cáp region.
A NE trending mineralized corridor in
which more than 15 areas of known artisan mines operating for past 10-20 years,
was identified recently. An alkali porphyry style of mineralization has also
been discovered in a new area known as
I. PU SAM CÁP PROJECT
AREA
The Mineral Exploration License Areas (MELAs) in Pu Sam Cáp Project
consists of MELA No.1 (70 km2) and MELA No.2 (84 km2).
The MELAs is centered on Pu Sam Cáp mountains, approximately 330 km northwest
of the Hà Nội capital, 40 km southeast of
Figure 1. Location map
II. EXPLORATION METHODS
The advanced technologies of GIS (Geographical Information System) and DBMS (Database Management System), together with the knowledge of the experts and consultants on many geoscientific fields have been applied for all stages of the exploration program. The main stages include reconnaissance, follow-up and targeting. The methods are used systematically and flexibly for consistent with the stages and the locations of project.
The main methods used by the stages of program are showed below (Fig. 2).
Figure 2. Exploration methods
Beside common geological methods (e.g. mapping, sampling…), the remote
sensing and geophysical ones have contributed remarkable results.
The remote
sensing method uses not only aerial photos, but also satellite images. The
kinds of satellite images are Landsat 7TM with 7 bands and 30 m spatial
resolution, Aster VNIR with 3 bands and 15 m spatial resolution, and Quickbird
panchromatic image with 0.61 m high resolution. By processing and interpretation
of these images, many useful information on lithology, structure, alteration
were gained. Especially, after geodetic survey, the ortho-rectification of
Quickbird image by using the WGS84 Việt
The geophysical methods has been applied both airborne and ground
survey ones. The first modern airborne geophysical survey was used in Northwest
Việt
The second
geophysical survey was surveyed by the Division of Geophysics of DGMV. This is
the first time a modern IRIS VIP.3000 transmitter and ElrecPro receiver
instrument were used for the IP/Resistivity survey in very difficult condition
of Northwest Việt
III. GEOLOGY AND
GEOLOGICAL STRUCTURE
A collecting and classifying work of previous geological data in conjunction
with recent surveys and examinations of the project has been carried out, and a
geological map have been drawn for the whole MELAs.
The Pu Sam
Cáp MELAs lie in the western part of the Tú Lệ volcanic depression which
follows a northwest trend, close to a major tectonic triple point, where three
paleo-continental plate boundaries appear to intersect. The Burma-Malaya plate
lies in the west, the South China Plate in the north and the
The
published 1:200,000 geological map indicates a volcanic centre, named as the Pu
Sam Cáp Complex, extending over an area some 7 km wide and 11 km long, bounded
in the east and west by regional-scale faulting. This Paleogene complex is
emplaced within a northwest-trending zone containing Triassic and Cretaceous
basinal and platform sediments, which now outcrop in an asymmetric anticlinal
structure, that dips gently on the southwest and steeply on the northeast of
the faults bounding the complex.
The Lower
Triassic C̣ Ṇi Formation consists of claystone, marl, sandy siltstone and
minor conglomerate. This is succeeded by the Middle Triassic Đồng
Giao Formation, which consists of light grey, thick-bedded to massive limestone
interbedded with siltstone lenses, shale, calcareous conglomerate and clayey
limestone. The Upper Triassic Suối Bàng Formation outcrops on the
northeast side of the Pu Sam Cáp Complex. It is a near-shore, upward-fining,
clastic sequence comprising a basal bed of conglomerate, gritstone, sandstone,
siltstone and clayey shale grading upward into clayey shale, siltstone,
sandstone and coal seams. The overlying Upper Cretaceous Yên Châu Formation
includes conglomerate, sandstone, siltstone and claystone, grading upward into
conglomerate, sandstone, siltstone, claystone and gypsum lenses and in the
upper part - conglomerate and sandstone. It occurs largely on the west of the
Pu Sam Cáp Complex.
The DMGV
mapping work indicates that the Pu Sam Cáp Complex comprises intrusive and
extrusive rocks emplaced within the Triassic and Cretaceous formations. Two
extensive areas of tuff, agglomerate and intrusive rocks occur, separated by an
east-northeast fault zone. In the north of the fault the pyroclastic rocks are
surrounded by arcuate outcrops of trachyte, feldspar porphyry and breccia,
forming an apparent ring structure which is in the southeast, in contact with
syenite and syenite porphyry. Small bosses of the latter are also mapped as
intruding the trachytes and tuffs. To the south of the fracture, the syenitic
rocks are flanked by trachytic rocks. It is possible that the trachyte and
syenite are different phases of a single, evolving magmatic event. A
cross-section on the unpublished map by the DGMV shows the igneous and
pyroclastic rocks as rootless, but they more probably represent a central
volcanic complex with brecciated ring dykes and subvolcanic intrusives. Coarse
and fine grained dykes containing locally greater than 50% biotite with
plagioclase laths predominating over orthoclase and minor black amphibole are
common throughout the area and have been assigned to the field name “minette”.
In a single outcrop the biotite content can vary considerably. They vary in
trend from east-northeast to northwest and are frequently intimately associated
with mineralization.
Data from previous geological maps and the TPJ’s interpretations from
remote sensing and geophysical data conjunction show that the MELAs is
controlled structurally by early NW regional fault systems and late NE fault
systems. The presence of late alkaline magmatic activities of the Pu Sam Cáp Complex in the MELAs centre is a
predominant potential for mineralizations of this region (Fig. 3).
Satellite
imagery shows that the Pu Sam Cáp Complex is crossed by prominent NE-trending
topographic lineations; the trend of these lineations is followed by magnetic
lineations derived from an airborne magnetic survey.
In
addition, the Pu Sam Cáp Complex is clearly outlined by the airborne
geophysics. The core of the complex has associated magnetic highs reflecting intrusives,
and is bounded by northeast/southwest striking structures..
Figure 3. Location of Pu Sam Cáp Complex on 3D Landsat 7TM drape image
Within the complex there are number of intrusives, including various syenites, feldspar porphyries and lamprophyres, which have been emplaced at different times. The potassium highs in radiometric survey which is centered in MELAS also affirm more clearly about the presence of alkaline magmas.
Following a study of faulting controlling the mineralization in the volcanic-hosted Pu Sam Cáp from 26 January to 5 February, 2007, R.H. Findlay, an expert on geological structure who has been working in Việt Nam for long time, after visiting the Pu Sam Cáp region reported that the prospect area is underlain by the Pu Sam Cáp Complex, an alkaline volcanic complex containing, seen by him, a purple hematite-rich volcanic breccia, a light-grey syenitic volcanic breccia and lamprophyric dykes. The Pu Sam Cáp Complex has been attributed to Paleogene-Neogene age, which leads to believe, through conversation with colleagues from the Research Institute of Geology and Mineral Resources, that it has been revised as 28 Ma through K/Ar dating by Vietnamese geologists. The volcanic complex overlies unconformably, and is also faulted against Cretaceous red beds (siltstone, sandstone and conglomerate) and unconformably Paleozoic formations deformed by the Indosinian Orogeny. And the study area and adjacent areas show unequivocal evidence for young, rapid uplift. The valleys are commonly deeply incised and show relics of older erosion levels perched on ridges; the hillsides are over-steepened, indicating no equilibrium between uplift and erosion rates; and in the Phan Si Pan area mountain slopes rise abruptly and approach the vertical. These general considerations lead the authors to believe, through comparison with topography in rapid uplift zones of New Zealand and Papua New Guinea, that uplift rates are or have been being of the order of 2 mm/yr and probably greater and that uplift occurred probably during the last 3 million years. This again bears on the general setting of the Pu Sam Cáp Complex; the volcanites could be well extruded at lower altitudes with a totally different hydraulic regime than present one, and it is correspondingly less easy to confirm the tectonic setting for the 28 my old volcanism.
Based on their studies around Băi Bằng, Xà Khoang and New Mining
areas the authors confirmed that generally least one major fault can be
expected to extend NE from the Thang Mine in the New Mining area, through Nậm
Beo and towards the Băi Bằng area, where it joins one of the NE trending
magnetic lineaments, and that other faults trend ENE and ESE. This pattern is
strongly suggestive of the Riedel shear pattern for a strike-slip fault array
and on geometry alone it would favour a dextral sense of displacement for this
system. The notion of strike-slip faulting is supported very strongly by the
prominence of shallowly plunging slickenside (generally grooves and ridges, or
scratch lineations) on a great many of the faults studied. In the main, the
mineralization of the fault surfaces was not lineated, indicating that it is
either younger than the faulting or occurred at a very late stage during
faulting.
IV. EXPLORATION RESULTS
A region reconnaissance program started early using Newmont methodology for BLEG sampling. This was complemented by pan concentrate sampling and rock chip (RC) sampling of mineralized float and outcrop samples and semi-detailed geological mapping throughout MELAs. Follow-up exploration work has been be on-going with more detailed BLEG sampling, RC sampling, mapping and ridge and spur soils on 50 meter centres to more closely delineate the in-situ source of mineralization. Simultaneously a targeting phase has been started to concentrate on mineralization zones with detailed mapping, RC sampling, test pit and trenching, ridge and spur and grid soil sampling and target drilling.
The results of exploration program have showed several prospect areas in
the MELAs from which have got potential mineralized features such as: Zone 5-7,
According to Eric Jensen (2005), a world expert on alkaline epithermal
system, the style of mineralization mined by local people is structurally
focused, small and is more characteristic of an Iron Oxide Cu-Au system (IOCG)
based on extensive feldspar-hematite alteration in upper levels, dominance of
specularite in zones of mineralization and presence (abundance) of deeper Na-Ca
styles of alteration rather than a more typical alkalic epithermal style
mineralization as observed at Cripple Creek. On the positive side, we have a large area with highly anomalous
gold in streams, a complex igneous / hydrothermal history with the upper
portion of system(s) preserved and a dominance of low-T hydrothermal features
as well as higher-T environments (skarn, porphyry?) seen in deeper levels of
exposure with possible juxtaposition or structural imposition possible.
The program has systematically mapped and sampled along a 5 km long,
northeast trending mineralized corridor. This corridor hosts at least 15 areas
of known artisanal mining that have been active for the past 10-20 years.
Results from recent rock chip samples taken from within this corridor
have revealed values of up to 126 g/t Au with highly anomalous base metals.
Individual auriferous structures within the corridor can now be traced over a strike
length of 3 km.
Detailed rock chip sampling along the structures has shown that
significant gold mineralization can be found within localized high grade
shoots. Two areas of interest have been selected within this corridor; the
first area is the New Mining Area, where intensive local mining is targeting
structurally controlled bonanza gold. The second area is composed of Zones 5-7
where recent drilling has intersected a structure which assayed 2m @ 7.8 g/t Au
and 0.63% Cu. This structure can be traced for over 1 km of strike length and
will be targeted for drilling.
Alkali porphyry style mineralization has also been identified in a new
area known as the
The recent ground geophysical survey results showed some IP anomalies in
Băi Bằng and
Below Table 1 are summaries of evaluating prospect areas.
The evaluation showed that the northeast trending mineralized corridor
which consists of Zone 1-3, Zone 5-7 and New Mining areas was a Cu-Au
mineralization style of IOCG system and the most area of artisanal mining.
However the anomalous results were concentrated in minor mineralization zones
as narrow, irregular and discontinuous veins.
The drill core assay results returned from these areas are disappointed,
only one positive result has come from a drill hole in Zone 5-7, but this is a
localized high anomaly in steeply dipping complex structure.
Figure 4. Pu Sam Cáp geological map
Table 1. Prospect areas of Pu Sam Cáp Project
Location Feature |
Zone 5-7 |
|
New
Mining |
Can Hồ |
Zone 1-3 |
Geology |
Volcanic breccia variety, lamproprophyre (Fig.5) |
Multiple intrusions: Syenite/Monzosyenite? (Fig.6) |
Syenite, lamprophere intruding Yên Châu sediments. |
Fault contact of limestone (Fig.7) |
Lamproprophyre intruding volcanic breccia , |
Structure |
Intersection of North East and East West |
North East and North South |
North East coss |
Splays off major NW |
North east Narrow and limited strike length |
Geochemistry |
Au, Ag, Cu, Sb, ±Pb |
Au, Cu, Ag, Pb, Sb, Mo, As |
Au, Cu,Bi,Ag |
Pb-Zn-Ag-(Cu) |
Au-Cu-Ag-Mo-Bi-Pb |
Geophysics |
Edge of magnetic high, IP Anomalies |
Low magnetics between large magnetic highs, strong
opened IP anomaly |
Localised subtle NE trending; Small IP anomalies |
Intense magnetic low, isolated highs to south west |
Mostly magnetic lows with localised magnetic high |
Alteration and mineralization |
Minor zones of K-feldspar→chlorite-pyrite overprint hematitic matrix in volcanic breccia. Quartz-carbonate-specularite-chalcopyrite-pyrite-gold
occurs as narrow, irregular and discontinuous veins |
Alteration/mineralization typical of
intrusion-related hydrothermal systems; Stockwork/sheeted vein systems of
variable intensity (Fig.6) |
Occurred along narrow structures (specular
hematite with carbonate + chalcopyrite + pyrite |
Massive Pb-Zn replacement, structural
intersections |
Minor zones of K-feldspar |
Target
style |
IOCG systems |
Porphyry Cu-Au systems |
IOCG systems |
Massive sulphide |
IOCG systems |
Here
are some typical photos taken from the prospect areas.
Figure 5. Zone 5-7 drill core, volcanic breccia variety
This said by Peter J. Pollard, an expert on mineralization who has just
researched mineralized features of the MELAs it seems to be lack of economic
potentiality. And in Can Hồ area,
a potentiality of massive sulphide was disappointed by grid soil sampling
program. But in contrast with these areas,
· Cu and Au geochemistry
· Most intense stockwork/sheeted vein zones
· Target high magnetics (hydrothermal magnetite)
·
CONCLUSIONS (from 2 year report)
The
dominant style of mineralization throughout the area mined by the artisans is structurally
controlled, complex and is more characteristic of an IOCG system based on
extensive feldspar-hematite alteration in upper levels, dominance of
specularite in zones of mineralization and presence (abundance) of deeper Na-Ca
styles of alteration rather than a more typical alkalic epithermal style
mineralization as observed at Cripple Creek.
On
the positive side there is a large area (region) with highly anomalous gold in
streams, a complex igneous / hydrothermal history with the upper portion of system(s)
preserved and a dominance of low - temperature hydrothermal features as well as
higher - temperature environments (skarn, porphyry?) seen in deeper levels of
exposure with possible structural juxtaposition.
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of Geology and Minerals of Việt
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