The Laredo limestone deposit is located on the eastern side Aristazabal Island, approximately 38 kilometres northwest of the community of Klemtu.
The area is underlain by a roof pendant of limestone is enclosed in hornblende diorite, monzonite and gneiss of the Tertiary to Jurassic Coast Plutonic Complex. It outcrops along the northeast coast of Aristazabal Island just north of Quarry Bay southeastward for 1.8 kilometres, and extends inland for 5 kilometres. The limestone is intruded by a few northwest trending, steeply dipping granodiorite dikes averaging a metre in width, and by a small stock of hornblende diorite along the shore at Quarry Bay. A northwest trending fault cuts the limestone along Quarry Bay. North of Quarry Bay, banding (bedding?) strikes north-northeast and dips 55 to 60 degrees west. To the south, the banding strikes northwest (308 degrees) and dips 35 to 65 degrees southwest.
Locally, the deposit is comprised mostly of snowy white, coarse-grained high-calcium limestone (marble) with some light to dark grey, fine-grained variably dolomitic bands 0.02 to 1.25 metres thick. A bed of dolomitic limestone outcrops on the western and southwestern portions of the deposit with a surface width of approximately 200 metres. The limestone is contaminated by variable amounts of pyrite, pyrrhotite, forsterite, serpentinite, spinel and graphite. A sample composed of chips taken at 0.15 metre intervals across a 12 metre thick band of coarse-grained white limestone in the quarry on the southeast corner of Lot 299 contained: 53.93 per cent CaO, 1.33 per cent MgO, 0.17 per cent insolubles, 0.09 per cent R2O3, 0.05 per cent Fe2O3, trace MnO, 0.01 per cent P2O5, 0.002 per cent sulphur and 43.75 per cent ignition loss (Geology, Exploration and Mining in British Columbia 1969).
Proven (measured geological) and probable (indicated) reserves have been determined for two zones within the deposit. Area 1 is estimated to contain 9.5 million tonnes of proven reserves and 10.0 million tonnes of probable reserves of calcium and high calcium limestone respectively; while Area 2 is estimated to contain 5.25 million tonnes of proven reserves and 36.0 million tonnes of probable reserves of calcium and high calcium limestone respectively (Property File - Rotzein, J.L., 1989).
In 1952, 10,886 tonnes of limestone averaging 98 per cent CaCO3 was quarried by Wood & McLay Limited. In 1969, Laredo Limestone Ltd. acquired 6 limestone leases and conducted stripping and quarrying. Reserves were estimated at 18,000,000 tonnes per 30 metres of depth. In August 1972 Kamad Silver Co. Ltd. acquired the property. In 1973 they drilled 25 holes totalling 38 metres. Laredo Limestone Ltd. had planned to commence quarrying in early 1990 at a rate of 8000 tonnes per day.
In December 1990 Laredo Limestone Ltd. drilled one hole and collected 24 surface samples in Area 3, between Areas 1 and 2, to confirm the continuity of limestone along strike and dip of the limestone beds, and upgrade the amount of reserves. The proven reserves were upgraded to 16.25 million tonnes high calcium limestone and 12.50 million tonnes limestone for the combined Areas 1, 2 and 3. Probable reserves were upgraded to 20.50 million tonnes high calcium limestone and 22.75 million tonnes limestone for the combined Areas 1,2,and 3. The total proven and probable reserves are 36.75 million tonnes of high calcium limestone, and 35.25 million tonnes limestone, for a total of 72.00 million tonnes. In 1994, a new owner, North Pacific Stone, resampled the area to better define the specific areas of high calcium limestone on the property.
The Laredo 1, 2, and 4-6 claims are held in good standing until late in 1999 by North Pacific Stone Limited of Surrey. They drilled 28 holes totalling 760 metres in 1999. Orinda Investments and North Pacific Stone plan to develop the deposit as a source of high-brightness filter for the plastics, paper and paint industries.