Despite being an established gold-producing region, the Dolgellau Gold Field is considered to be underexplored, with most of it yet to be the subject of sustained modern exploration at a regional scale, in terms of the use of methods such as low detection limit geochemical soil sampling, close-spaced ground and airborne geophysical surveys and drilling.
Alba has completed an extensive, regional scale geochemical soil sampling programme, which identified 10 significant gold anomalies over a six-mile section of the Dolgellau Gold Belt. These have since been refined to six major targets.
The largest gold anomaly identified is about two kilometres long, four times longer than the length of the equivalent anomaly over the historic Clogau-St David’s Mine.
Alba has also discovered potential extensions to the existing footprint of the historic mine area, with infill sampling confirming continuity of an anomaly, Lowri, lying parallel to the Llechfraith adit and a major anomaly, Eryn, lying above historic Llechfraith workings.
A high-resolution UAV (unmanned aerial vehicle) aeromagnetic geophysical survey is currently being undertaken across certain high priority gold targets within the Dolgellau Gold Belt. The survey objective is to pinpoint the bedrock sources of geochemical anomalies, to gain a better understanding of regional geology (bedrock and faulting) and to target lodes and mineralisation. The results could contribute significantly to both regional exploration and the identification of further near-mine resource opportunities. The survey should enable Alba to define targets with enough confidence to undertake follow-up investigations such as drilling.
The survey encompasses:
Once UAV aeromagnetics have been used to delineate target structures, detailed soil sampling programmes can be rolled out to test whether these structures have the potential to host mineralisation in economic quantities and grades.
The Hafod Owen Prospect plays host to a potentially widespread epithermal gold system. An outcrop in this region shows an example of breccia mineralisation, which historically graded 2.9 g/t Au and an Alba sample of nearby float was assayed at 3.8 g/t Au.
Two notable historical mining operations have taken place, at Foel Wen and North Dolfrwynog. The former is on the western extent of the target area. Spoil tip material here shows exceptionally copper-rich quartz vein material with appreciable gold credits.
The latter, North Dolfwrynog, was comparatively more extensive and although ultimately unsuccessful was noted to have worked both N-S and E-W lodes. A boulder found on a presumed spoil tip showed epithermal-style banded quartz veining and hosted pods of gold-bearing sulphides within the vein, with a representative sample of the boulder grading 6.53 g/t Au and a sample targeted on the sulphides grading 24.1 g/t Au.
With the pronounced alteration at the Hafod Owen prospect, it is hoped that aeromagnetics will be effective at pinpointing vein and breccia-hosted mineralisation concealed beneath overburden and forestry land.
Alba’s 2019 regional reconnaissance programme identified several poorly understood mineral occurrences in the Afon Gain catchment region. Several key drainage basins were identified in this region through the analysis of historical stream sediment data. Subsequent field work in 2021 confirmed the presence of two notable trial mining efforts on either side of the Afon Gain. A sample from the main adit tip returned assays of 0.143 g/t Au, 33.7 g/t Ag, 1.115 % Cu, 4.25 % Pb and 2.39 % Zn, and an additional sample from the upper tip close to surface excavations graded 2.43 g/t Au, 15 g/t Ag and 1.22 % Cu.
The largest site has two adits driven northwards into the hillside, each with notably large spoil tips. Aeromagnetics should be able to penetrate this cover and potentially identify the true extents of the mineralised lodes, with the chance of delineating additional lodes and even potential large scale feeder structures, giving Alba the first true view of the subsurface in this prospective and underexplored region of the Dolgellau Gold Field.
A prospective location within the Afon Gain target
Castell Carndochan is a 19th century gold-silver mine near Dolhendre. The mine was discovered in 1862-3, and operations continued sporadically until the eventual cessation of work in 1904-5. Published production grades have suggested that ~7068 tonnes of quartz ore were produced at an average grade of 11.7 g/t Au, although production grades as high as 153.6 g/t Au were recorded in the early days. The host stratigraphy is thought to extend up to 400 m underneath adit level, suggesting significant potential for resources at depth.
At least two underground levels at Carndochan are accessible, with evidence of lower flooded workings. Assay results have returned high-grade gold-silver, with significant zinc-lead credits. Notably, sample CCD-02 returned grades of 20.6 g/t Au, 27.1 g/t Ag, 1.175 % Pb and 0.257 % Zn and sample CCD-03 1.63% Zn and 0.392 g/t Au.
The aeromagnetic survey being undertaken will allow Alba to map bedrock lithologies with unprecedented accuracy, with the primary goal being the identification of structural features that may host gold-mineralisation.
High-grade gold sample taken from Carndochan
The Caerwych Prospect is the most recent addition to the list of high priority gold targets within the Dolgellau Gold Field. The area has had historical mining activity, with several mines centred around a series of NE-SW trending structures.
This prospect is likely to have similar mineralisation styles to the Afon Gain Prospect due to their proximity. It is currently unknown whether the large historically mapped NE-SW faults host mineralisation or are a later sub-parallel stage of faulting that cuts mineralisation. An aeromagnetic survey would help to establish this structural framework and identify prospective structures for follow-up work.
The Caerwych Prospect