The Merléac PER covers 411 square kilometres over the eastern end of the Châteaulin Basin, a sequence of felsic volcanics and clastic sedimentary rocks containing base and precious metal deposits. One of the key deposits within the basin is the Porte-aux-Moines volcanogenic massive sulphide (VMS) zinc-lead-copper-silver-gold deposit which lies near the centre of the Merléac licence about 125 kilometres west of Rennes, Brittany.


Porte-aux-Moines (PAM) is a classic VMS deposit believed to have formed on or close to the sea floor during a volcanic-associated hydrothermal event. The deposit shares many geological similarities to other VMS deposits in Australia such as Woodlawn, Rosebery and Que River which have been important sources of high grade base and precious metal production (for an indication of sizes and grades of these refer to the following table extracted from the US Geological Survey (USGS)).


Tonnes and grades of selected VMS deposits in Australia

Table 1

USGS site address - download


As with many VMS systems, PAM may be one of a cluster of individual sulphide deposits that are frequently formed in close proximity to one another and which can generate sizable tonnages of high grade mineralisation.

PAM was discovered by regional stream sediment sampling and follow-up drilling in 1975/76 by the BRGM (Bureau de Recherches Géologiques et Minières - the French geological survey). During the late 1970's and early 1980’s the BRGM completed considerable exploration over the deposit including 6,843 metres of surface core and 2,830 metres of underground drilling. It also completed about two kilometres of underground decline development to 150 metres below the surface including five crosscuts through the ore system to provide detailed geological data to assist in resource estimation and metallurgical sampling. 

The work outlined zones of high grade lead-zinc-copper-silver mineralisation up to 20 metres thick from surface to a depth of about 300 metres over a strike length in excess of 250 metres. Aside from the underground development and sampling the deposit is essentially unmined.

In 2015 the Company accessed three remaining surface core holes from the BRGM exploration of PAM stored at their Orleans core farm. Resampling of mineralised intervals was completed and samples sent to ALS Geochemistry for confirmatory reassay. Results from this work confirmed the high grade nature of the deposit with strong, zinc dominant, polymetallic intersections recorded in all holes.

Importantly, the ALS assays were, on average, slightly higher grade than the original BRGM assays, confirming the general overall accuracy and the high quality of the BRGM work. This provides high confidence in the veracity of the BRGM assays for the remaining drilling and underground development.


The VMS mineralisation at PAM is broadly contained within a sequence of sediments and volcanics. Mineralisation occurs as multiple, disrupted sulphide lenses, mainly hosted by black shales and cherts. 


Porte aux moines diagram 2

Plan view of the Porte-aux-Moines deposit showing interpreted mineralised zones
underground development completed by BRGM. 


Massive sulphides are very pyritic, with three main zones of mineralisation modelled to date from the BRGM data.

Main Zone: This is the lowest stratigraphic horizon and is generally located at the interface between the volcanics and overlying host sediments, but is currently modelled to migrate into a more hanging-wall position to the east. The Main Zone can be subdivided into a thick zone of high grade mineralisation (approximately 16 metres wide) that appears to have been deposited on the sea floor within a shallow depression, and thinner flanking mineralisation lateral to the thickened zone.

HW1 Zone: Mineralisation located up to about 20 metres into the hanging wall of the Main Zone. It is smaller and lower grade. However, the HW1 zone is laterally extensive and appears to have potential to extend to the west and down-dip.

HW2 Zone: A small zone at the western end of the deposit.


 Porte aux moines diagram 3

Vertical long section of the Main Zone surface at Porte-aux-Moines showing the
thickened zone and flanking mineralisation. Proposed deeper drilling
pierce points shown as well 
as the target area for shallow drilling (hatched).


Porte aux moines diagram 4

Cross section through Porte-aux-Moines showing interpreted mineralised zones 
and proposed future drilling.


Porte-Aux-Moines Mineral Resource

In June 2016 the company published a maiden Mineral Resource reported to 2012 JORC.

The Mineral Resource is 2.2 million tonnes grading 6.0% zinc, 1.3% lead, 0.8% copper, 80.6 g/t silver and 0.9 g/t gold.

 Porte aux moines diagram 5

Note: Mineral Resource is based on a zinc cut-off of 8.0% Zn Eq. Calculations have been
rounded to the nearest 1000 t, 0.1 % zinc, lead and copper grade, 0.1 g/t gold and silver grade.


The Mineral Resource estimate was completed by QG Australia Pty Ltd, an independent consultancy group that specialises in resource estimation for deposits like Porte-aux-Moines, from mineralisation domains and wireframes supplied by Variscan geologists. The geological model and Mineral Resource estimate were based on 58 surface and underground diamond drill holes, mapping and assays from underground development to the -150 metre level as well as data from a number of shallow percussion drill holes completed by the BRGM.

Data density for the deposit is variable with drilling completed on nominal 100 metre centres in the upper parts of Porte-aux-Moines, down to 20 metre spacings (or less) in areas of combined underground development and drilling.

Further drilling is required to confirm the geological interpretation, increase the tonnage of Indicated Mineral Resource and provide additional samples for confirmatory density measurements and gold assays. In the short term, deeper drilling is planned to test the thickened Main Zone and deeper parts of the HW1 zone.

In addition, later drilling may also infill the thinner, but shallower section of the Main Zone close to the surface, which has had little exploration in the past. There is good potential in this area to expand the Indicated resource above the level of the former underground development.

Modelling work by Variscan indicates that approximately 3.5+ million tonnes of resource will be required to justify initiation of mine feasibility studies. Growing the size and enhancing the classification levels of the current 2.2 million tonne resource base to a level sufficient to allow the company to move into feasibility studies is a key priority.


Porte aux moines diagram 6

Global ranking of projects and mines by grade and size compared to the mineral
resources of about 300 zinc and polymetallic mines and projects worldwide. The
zinc equivalent grade calculation represents the value for each metal - Zn
(US$1,800 per tonne), Pb (US$1,800 per tonne), Cu (US$5,600 per tonne), Ag
(US$15 per ounce) 
and Au (US$1,150 per ounce) - multiplied by the grade and
estimated metal recoveries 
(Zn–90%, Pb–85%, Cu–80%, Ag–60%, Au–70%),
summed and expressed in equivalent zinc percent per 
tonne. The zinc equivalent
calculation is intended as an indicative valueonly. Source: Terra Studio


Regional Exploration

The regional potential within the Merléac licence for additional VMS deposits is considered excellent. PAM is hosted within a sequence of vitric tuffs and pyritic black shales (the mine sequence) located in a bimodal sequence of felsic and intermediate/mafic volcanics. This sequence of rocks can be traced for approximately 80 kilometres along strike and within structurally repeated blocks in the Merléac licence.

Within these rock units outcropping gossanous zones containing highly anomalous base and precious metal values have been defined interpreted to represent the oxidised expressions of underlying sulphides. Some of these gossans were previously mined by shallow open pits for iron up until the 19th century and generally have not been explored below the iron oxide cap aside from BRGM drilling in some locations.

In September 2015, Variscan announced that it had completed modelling of a large, heli-borne, VTEM survey. The survey was designed to test the key target VMS mineralisation areas in and around PAM and within the broader Merléac licence. The survey covered approximately 160 square kilometres of the southern section of Merléac, testing about 50 strike kilometres of the Porte-aux-Moines host stratigraphy.

The survey:

  • Detected the PAM deposit, which clearly stands out as a bulls-eye anomaly with a modelled strike length of about 400 metres.
  • Successfully identified 14 high priority 'Tier 1' targets with moderate to strong, early to late time EM responses, in many cases similar to those generated at PAM and which are possibly caused by sulphide-rich bedrock sources.
  • Identified approximately 50 other conductors that may be due to sulphide zones but are close to buildings, power lines or other 'conductive' infrastructure, which requires field checks to confirm the source of the anomalism.

  Tier 1 VMS Targets

 'Tier 1' VMS targets over Channel 40 response plot at Merleac


Recent follow-up exploration of the VTEM and geochemical targets as well as review of previous exploration work has provided strong evidence that additional new VMS deposits will be discovered within the same rock sequences that host PAM.

Two main trends (PAM-Gausson and Le Roz) over a total strike length of 22 kilometres hosting seven centres of base metal mineralisation have been defined, with highly geochemically anomalous rock chip/grab results recorded in new sampling. At some prospects these assays are in proximity to strong VTEM anomalies, interpreted to be possible buried VMS deposits.  

PAM - Gausson Trend

This extensive east-west striking zone is the most important defined to date and stretches approximately 15 kilometres from PAM to the Gausson prospect in the east. Five main areas of VMS mineralisation have been defined within sediments and volcanics along the general PAM VMS deposition horizon.


 Porte aux moines diagram 8

Key VMS prospects within the Le Roz and PAM-Gausson mineralised trends. Summary
of BRGM geology.

La Pris Mallard Prospect

This prospect also includes a "Tier 1" VTEM anomaly located about 5 kilometres east of PAM. Previous BRGM work included shallow percussion and core drilling which recorded base metal sulphides and strong sericite-quartz-pyrite altered volcanics just west-south-west of the strong VTEM anomaly.

Rock chip/grab samples from gossanous material representing oxidised semi–massive and massive sulphide and stockwork sulphide-veined material recorded individual assays of up to 6.1% lead, 800ppm zinc and 1840ppm copper were recorded, confirming this as a likely centre of VMS mineralisation.

Les Essarts Prospect

This advanced prospect is approximately 700 metres in strike length and was drilled to a shallow depth by the BRGM during the 1970's. The drilling recorded a number of zinc-lead-copper intersections of stratiform VMS mineralisation including - 

  • 1.25 metres @ 7.0% zinc, 3.04% lead, 0.22% copper from 80 metres in LSS2, and
  • 1.0 metre @ 5.49% zinc, 2.72% lead and 0.26% copper from 66 metres in LSS3

The BRGM work has clearly identified another centre of VMS mineralisation broadly analogous to PAM.

This will be one of the priority targets for additional Variscan exploration work.

Les Forges Prospect

The prospect lies approximately 1.2 kilometres east of Les Essarts. Previous work by Variscan included sampling of a group of old iron workings that mined gossanous material displaying box-work textures after base metal sulphides.

Highly elevated results up to 1986ppm zinc, 318ppm lead, 638ppm copper and 260ppb gold were recorded over a strike length of about 700 metres, again believed located within the same rock package that hosts PAM.

Gausson Prospect

Former work by the BRGM included shallow drilling to the southwest of a strong VTEM anomaly, intersecting low grade stockwork copper mineralisation.

Recent Variscan rock chip and float sampling (including the VTEM target) returned elevated surface values, believed associated with VMS mineralisation, up to 875ppm zinc, 1991ppm lead, 917ppm copper and 90ppb gold.

Le Roz Trend

This newly defined trend lies approximately two kilometres south of the PAM deposit and has been defined on the basis of a string of strong VTEM anomalies. To date Variscan has assessed two of the seven 'Tier 1' VTEM anomalies that have been defined over a strike distance of around seven kilometres. Both anomalies, Le Roz and Kervegan do not appear to have been explored previously and are favourably located within the interpreted folded repeat of the PAM mineralised rock sequence.

Base metal geochemistry at both prospects is elevated, particularly at Le Roz, indicating the possible presence of base metal sulphides.

Download Report

Please click here to see the Porte-aux-Moines Report