GSSL Pleasure Trip to Seruwila Copper-Iron Deposit

By Mr. Nimal Ranasinghe–

Preliminary investigations of the Seruwila Copper-Iron mineralization commenced in early 1971 by the Geological Survey Department (GSD), the predecessor to the Geological Survey and Mines Bureau (GSMB). I recall that, the GSD was then scheduling a magnetometer survey to assess the Buttala-Kukurampola magnetite occurrence that was discovered by Geologist L.K.Seneviratne in 1967, on July 8^th to be precise, and had to be postponed in favour of the Seruwila investigation.

The geologist for the initial Seruwila probe reported the area was very difficult of access due to thick jungle and teeming swarms of mosquitoes. But based on his encouraging report, many detailed investigations were done that led to the 18-month long detailed integrated investigation from July 1979 to early 1981 in collaboration with the French Bureau de Recherches Géologiques et Minières (BRGM).

This joint investigation covered an area of 70km² and included detailed ground magnetometer survey, geological mapping, geochemical survey followed by an extensive programme of core drilling comprising 43 drill holes totaling 5,400m averaging 125m per drill hole to examine magnetic anomalies to confirm sub surface structural behaviour as revealed by detailed geological mapping. All activities carried out and data gathered along with interpretation, conclusions and recommendations and compiled in a 4-volume report is available for reference at the GSMB library.

To quote salient facts from the report, the Seruwila copper-magnetite mineralization that’s located in the Trincomalee District about 275 kilometres from Colombo best approached by the Kantalai-Allai road;

Mineralization occurs in three areas namely, Block ‘C’, Arippu and Kollankulam.
Block ‘C’ and Kollankulam reported rather disseminated mineralization and low copper values whereas Arippu mineralization showed greater concentration with higher copper values.
The only workable reserves are those of the southern Arippu strip that revealed 2.55 Mt of ore as Inferred category assaying 1.1% Cu and 42.3% soluble Fe over a depth limited to 200m.
The mineralized lenses dip very steeply or sub-vertical. Their lower limit is not known and cannot be deduced.
The mineralized strips striking 060⁰ is parallel to the main metamorphism and the mineralization considered as stratiform.
The mineralization is observed to straddle the Highland and Vijayan boundary and hosted by basic rocks of amphibolite-pyroxenite type. The ore consist of magnetite, chalcopyrite, pyrite, bornite, azurite, cubanite, malachite, pentlandite, sphalerite, hessite, traces of gold and fluor-apatite assaying nearly 25% by volume of the non-magnetite fraction.
The many suites of sulphides are inferred to imply a volcanogenic–sedimentary origin.
Of significance is the occurrence of anorthosite within the country rocks, a first time happening from this area.

This was the deposit we had planned to visit on the first day of the trip. As it was a visit since 1981, a period of 34 years and naturally, undergone considerable change over the years, I had arranged for two Seruwila locals who worked with us then to visit the magnetite outcrop and if it is still difficult of access, have a path cleared for us.

As I being the only member of our group who conducted the 18-month long project as one of the two counterpart Geologists to BRGM Earth Scientists, was eagerly looking forward to show the area and its key features. I was planning to show three features, which, during our project, was the cynosure of many visitors, they being; an ancient mining trench dug along a vertical joint as one wall (c. 150 BC), the one and only – mound-shaped – magnetite outcrop of about 4m high and 10m diameter, it was to be the main attraction and a very small flat exposure of anorthosite about a kilometre westwards of the magnetite.

Although I had given about two weeks’ notice for the two former workers, even up to the day of our departure, the news I received continually was very discouraging being that the two locals despite their determined search, even along with two others, was their failure to locate the outcrop which they attributed to substantial changes of landscape caused by new roadways, extensive clearing, both afforestation in new areas and reforestation that had disoriented even the locals!

So when we arrived, we had to depend on our archaeo-geology members who were able to locate an old trench. It was a shallow pit but nevertheless an old trench filled up over the years. Of note was the spread around the trench of small magnetite crystals and pieces apparently as discards after separating the copper ores. Both the old trench and the magnetite outcrop that I was eager to show remained elusive.

Thereafter, we visited the Seruwila Rajamaha Vihahara Temple and on the way to Trinco stopped about a kilometre from the temple, where I guessed as the location of the anorthosite occurrence. Although there were some whitish outcrops, they turned out be weathered granitic gneiss and no anorthosite was found. Here again, the whole area was completely transformed.

Needless to say, we left Seruwila with a heavy heart but with determination to find what we couldn’t, particularly the magnetite outcrop. Rather than passing the responsibility to the locals, it is fitting that the GSMB resolves to relocate at least the said major features and invite research by the local academia.

Nostalgically, I recalled the numerous visits made to this magnetite outcrop during the project and could still visualize its many features partly covered by overgrowing plants. I reminisced that in addition to geological and mineralogical features, the site was also used to demonstrate to the lay visitors the effect of a magnetic body on our field compasses. But despite all the thorough investigations made on it both by the GSMB and BRGM never did they ever found the slightest indication that it also had the ability to vanish into thin air within 3 decades! Indeed a challenge posed to the GSMB.