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 Nam for exploration activities. Its subsidiary Triple Plate Junction Limited (TPJ) is a joint venture between TPJ and Newmont Việt Nam Pty.Ltd (previously named as Normandy Anglo-Asian Pty.Ltd or NAAL).

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 Upper Nậm Đích. These results have been requiring new attempts of the project for concentrating an extreme effort to reach to success in the Pu Sam Cáp region.


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 Lai Châu Town and 15 km south of Tam Dương, located in Tam Dương, Śn Hồ and Than Uyên districts, Lai Châu province. This area is very rugged and mountainous with steep-sided gullies and valleys rising over 2,300 m from 400 m in the adjacent valley floors. The climate is dry to humid from late May to early October, with temperatures ranging from 20 to the low 30°C. From early October to late May the cold and mainly humid conditions prevail, with temperatures from 0 to 15°C. There is a marked wet season from July to October (Fig. 1).


 

 

 

 

 

 

 

 

 

 

 

 

 

 

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 Nam surveyed ground control points has been playing an important role as a base topographical map for working in the field. The drainage, tracks, roads, villages, plantation were extracted with high reliability and accuracy. The Aster that was used in conjunction with surveyed control points has been used to produce a DEM (Digital Elevation Model) that allows to view the whole area in 3D.

The geophysical methods has been applied both airborne and ground survey ones. The first modern airborne geophysical survey was used in Northwest Việt Nam in very difficult terrain. 3,165 km line of helicopter-borne magnetic and radiometric survey has been utilizing Newmont Mining Corporation equipments and operators, data processing and interpretation. Mean instrument ground clearance of 70 m in terrain has been ranging from 240 to 2,520 m ASL. Surveying was conducted on 200 m spaced lines over the broader tenement and 100 m spaced lines over the Pu Sam Cáp Complex. Several exploration targets defined as sites of potential intrusive- related and skarn style of mineralization and alteration.

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 Nam. The design, quality control and interpretation was carried out by a consultant of Planetary Geophysics Pty Ltd. The 100 m space of lines and the 50 m space of stations along soil grid lines were designed. Total of 25,050 m length of survey completed in 3 prospect areas: Băi Bằng (Zone 5-7), New Mining Area and Upper Nậm Đích. Some IP anomalies were discovered in three areas.

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 Indochina plate in the south, and it is considered likely that these three plates were joined in the Late Paleozoic. Several porphyry Cu and epithermal Au-Cu deposits in Việt Nam and China have been interpreted to lie on the extrapolation of this trend.

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, Upper Nậm Đích, New Mining, Can Hồ and Zone 1-3. There were many artisanal mines located in these areas (Fig. 4).

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 Upper Nậm Đích approximately 3 km to the south of Zone 5. Recent trenching results have returned 60m @ 0.44 g/t Au and 0.1% Cu within a 250 x 100 m coherent +0.05% Cu-in-soil anomaly in altered intrusive. Mapping and drilling are now in progress to better outline alteration, mineralization as well as intrusive phases.

The recent ground geophysical survey results showed some IP anomalies in Băi Bằng and Upper Nậm Đích areas. Several weakly IP anomalies in New Mining Areas which lies in NE mineralized corridor suggested a result that is consistent with Eric Jensen’s conclusion.

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

Upper Nậm Đích

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-feldsparchlorite-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, Upper Nậm Đích has been concentrating optimistic conditions forming large mineralization style of porphyry Cu-Au system. When surveying around Upper Nậm Đích area, Peter J. Pollard noticed that this is an intrusion-related Cu-Au system of major proportions. Possible vectors to mineralization were mentioned as follows:

·      Cu and Au geochemistry

·      Most intense stockwork/sheeted vein zones

·      Target high magnetics (hydrothermal magnetite)

·      Target Mo (-Cu-Au) anomalies (Mo commonly focused towards the higher temperature part of the system).

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.

REFERENCES

1. ACA Howe International limited, 2004. Satellite image interpretation for a study area in northwest Việt Nam

2. Barton M. D. and Johnson D. A., 2000. Alternative brine sources for Fe-Oxide (-Cu-Au) systems: Implications for hydrothermal alteration and metals. In Porter, T. M., ed., Hydrothermal Iron Oxide Copper-Gold & Related Deposits: A Global Perspective. 1, Australian Min. Found., p. 43-60.

3. Dept of Geology and Minerals of Việt Nam, 2005. Geological and Mineral Map, 1:200,000. Hà Nội.

4. Findlay R. H., 2007. Faulting at the Pu Sam Cáp prospect, Việt Nam. Internal Report. Geol. Archives, Hà Nội.

5. Phan Cự Tiến et al, 1991. Geology of Cambodia, Laos, Việt Nam. Gen. Dept of Mines and Geology, Hà Nội.

6. Pollard Peter J., 2006. An intrusion-related origin for Cu-Au mineralization in iron oxide-copper-gold (IOCG) provinces. Niner Deposita, 41: 179-187.

7. Satellite Imagery Applications for the Real World. WWW.Geoimage.com.au (GeoImage PTY Ltd)

8. Sexton M., 2006. Interpretation of helicopter-borne magnetic/radiometric survey at the Pusamcap Project, Lai Châu, Việt Nam. Internal Report.

9. Sexton M., 2007. IP/Resistivity surveys at the Pusamcap Project, Lai Châu, Việt Nam. Internal Report.

10. TPJ Staff, 2005-2007. Monthly Reports 2005-2007. Internal Report.