CATEDRAL HIGH GRADE LIMESTONE RESERVES & A POSSIBLE 500+ TPD LIME PLANT
The large tonnage of easily mined high grade limestone, the strategic location, the nearby gas line, as well as the shortage of suitable and accessible limestone in Chile, bly favour a lime producing operation at Catedral. The market study undertaken for SAGC’s new Quellon lime operation, shows there is a market opportunity in which the expected low cost and volume of lime production at Catedral could result in a very competitive lime producer.
The Catedral Project is located 80 km in a direct line south east of Santiago. The distance by road from Santiago is 110 km, with travel time taking approximately two hours. The last 48 km are unpaved.
The limestone belt in the project area corresponds to the upper part of the over 200 meter thick Cretaceous LoValdes Formation. The limestone beds dip steeply and are on the western limb of a broad anticline, which strikes 10 to 15 degrees north west and plunges gently towards the south. The extension of the limestone to the north is truncated from the younger sediments of the Colimapu Formation by a b N60E trending fault zone. A kilometre south of this break, a massive N30W fault called the Mona fault has distorted the limestone beds forming a zone up to 200 meters wide. From this point towards the south, the limestone formation is unaffected by large breaks. It extends for 6 km before passing out of Cia. Minera Catedral’s claims at an altitude of 3800 meters. In all, there are 8 km of LoValdez Formation limestone beds within the company claims.
At the northern end of the limestone belt and up to an altitude of 2300 meters, the rocks are largely covered by deposits of glacial origin. Good rock exposures occur to the south above 2700 meters. On the north-west trending Mona Ridge, there are good exposures of limestone over a length of 600 meters and a width of up to 150 meters (photo 3). This ridge lies parallel and immediately to the north of the b Mona fault referred to previously. Limestone exposures on the extension of the belt to the south, beyond the influence of the N30W fault zone, start 500 meters south of Mona Ridge at an altitude of 2750 meters. At this point the limestone is 215 meters thick.
The limestone is micritic to fossiliferous with varying amounts of carbon and autogenetic finely divided disseminated pyrite. Sandy intercalations occur. Colour varies from light grey to almost black. The beds are massive with CaCO3 content varying from 73% to 93%. High grade beds have been recognised by assaying, but can with practice also be recognised in the field. Beds with surface assays grading above 90% CaCO3 vary in widths from 11meters up to 30 meters and may even reach as much as 75meters.
Sampling of the Mona Ridge and South Mona limestone beds was undertaken to evaluate the potential for inferred reserves of high grade limestone suitable for lime production. With this in mind, a line of surface samples were taken across the limestone at Mona Ridge and at South Mona (photo 1 & 2). The maximum width sampled for individual samples was five meters. Samples weighed 5 to10 kilos and were assayed in Santiago by ALS Laboratories (Geolab).
On Mona Ridge, three high grade beds have been identified by sampling. (photo 1 & 3). Results are given below starting with the stratigraphically lowest and oldest bed in the east, and passing towards the west with successively younger beds:
Note: At Mona Ridge, Bed 1 is separated from Bed 2 by over 15 meters of lower grade limestone. Bed 2, with two lines of samples 90 meters apart (sample lines 2A and 2B) is separated from Bed 3 by 44 meters of lower grade limestone. Both Bed 1 and Bed 3 on their outer sides are in contact with lower grade limestone.
At South Mona, samples were taken 800 meters south of the east end of the limestone beds on Mona Ridge at an altitude near 2850 meters. At this point, the limestone is 215 meters wide and shows no modification by hydrothermal effects due to the presence of intrusives or mineralising emanations. Rock is exposed over 120.9 meters. Where possible, consecutive samples were taken across the strike (photo1). These totaled twenty nine samples. Assay results from these samples have established the presence of at least four well defined beds containing between 89.74 % and 92.94% CaCO3. As 94.5 meters of the 215 meter wide formation is masked by surface cover, further widths with over 90% CaCO3 may occur.
Details of the sampling results are given below, starting with the stratigraphically oldest bed to the east followed by progressively younger beds towards the west:
Note: It is possible Beds C and D may be parts of one larger bed, as there is an intermediate 5.2 meters of 89.58 % CaCO3 appearing within highgrade fossiliferous float separating the two beds. If this assumption is correct, total width could amount to over 70 meters. All four high grade beds are within low grade limestone. Some 46meters separate Bed A from Bed B, which is separated by 37 meters from Bed C, which in turn is separated from Bed D by 32meters.
INFERRED RESERVES MONA RIDGE AND SOUTH MONA
The probable continuity of high grade limestone between Mona Ridge and South Mona has been indicated by sampling in the two zones. In the Mona Ridge area the sampling is spread out obliquely over a length of 500 meters and breadth of 200 meters . In the South Mona area, high grade limestone occurs 800 meters to the south. This implies a probable horizontal continuity approaching near 1500 meters. These suppositions can be easily verified by further surface sampling next spring.
Inferred reserves, based on surface sampling and rock exposures, has been estimated by using extensions of 100 meters either side of where the samples were taken. This is provided there was enough exposure of limestone to justify the assumed extension. Depth extension has been taken at 100 meters, which is conservative on account of the steep topography with exposed limestone occurring over a vertical range exceeding 500 meters. The evidence for horizontal continuity already referred to also supports the supposition that a 100 meter depth extension is reasonable. Density has been taken at 2.7, which is on the low side for limestone. Average carbonate grades based on surface sampling tend to be a fraction lower than those found at depth due to surface leaching. The grades given in this preliminary report are regarded as reliable. Inferred reserves for the two areas are given below:
POTENTIAL HIGHGRADE LIMESTONE RESERVES
Black high grade limestone was encountered in two drill holes put down on Rino, 6 kilometers to the north east of the Mona area. The drill intercepts are at or near the stratigraphical level of the Mona limestone belt. The limestone at Rino is rich in carbon as proven by thin sections and cement kiln tests which showed energy consumption is 15% below normal on account of included carbon. Also, in flotation tests for pyrite removal, large amounts of carbon interfered with the flotation process. The presence of identical high grade black limestone at South Mona, in contrast to those of the Mona Ridge which are lighter in colour due to modification by a nearby, fairly large quartz feldspar intrusive, is a direct indication of high grade carbonaceous limestone being deposited over a wide area under uniform conditions.
This geological setting has a direct bearing on the potential tonnage of high grade limestone that can be expected in the area. It is clearly very large. In the Mona zone alone, taking the indicated length of 1500 meters, using the high grade sampled widths, and taking extension in depth to 200 meters, which is very conservative taking into account the known vertical exposures, gives an overall potential of just under 50,000,000 tons. Most of these potential reserves will have to be mined underground. As the limestone beds are wide to very wide, mining costs will be low with access by adits.
FURTHER WORK NEEDED TO SUBSTANTIATE HIGHGRADE LIMESTONE RESERVES
Exploration and development for reserves to adequately support a 500 tons per day lime producing operation will be restricted to a four hundred meter stretch of the 214 meter thick limestones at Mona Sur. Here the limestones are unaffected by intrusives or proximity to the Mona Fault. The four high grade beds or mantos located within the general limestone sequence will be topographically and geologically mapped at a 1:500 scale. There are two areas of extensive limestone exposure within the study zone. One has a horizontal length of 350 meters, containing high grade mantos A and B, and the other to the immediate west is 250 meters long within which high grade mantos C and D occur. The limestone formation strikes at N10W and dips towards the west at 85 degrees, it forms a prominent topographical feature in the form of a ridge that rises steeply to the south at thirty five degrees.
Surface samples of the limestones will be taken across rock exposures as far as possible on 50 meter centers. Individual samples will not exceed five meters in length.
While this work is proceeding the existing road, which reaches a point 200 meters below the Mona Ridge crest, will be extended three kilometers to reach the lowest projected 2850 meter mining level at Mona Sur. From this level to the west of the limestones, a 2100 meter road will climb first, to a drill station at 2920 meters, and then to a second at 3060 meters. On the east side of the limestones a drill station will be prepared on the 2850 level and another will be reached by 1400 meters of road to the 2990 meter level. The four drill holes will be up against the limestone contacts to minimise drilling through overburden. Horizontally they will be approximately 100 meters apart and they will be drilled at forty five degrees for 300 to 350 meters. Two holes will be drilled towards the west and two towards the east. Distances and elevations given are approximate.
The planned surface sampling and inclined holes will give two intercepts for each of the four high grade mantos along the four drill hole sections. As two holes are drilled in the opposite direction a third intercept can be projected on to the sections. Intercepts will vary from near surface down to approximately 230 meters below the surface. Provided there are no intrusives to modify the potential, the planned surface work and drilling, should give a proven and probable reserve, over a four hundred meter strike length, of approximately 12.000.000 tons. To complete the outlined work and using two drills, is expected to take six to eight weeks and cost US$ 122,000.
LIME METALLURGICAL TESTS
In all six surface samples of limestone have been sent from the Mona Zone to Cimprogetti in Italy for burnt lime tests. These samples were made up from the sample traverse run over Mona Ridge and that run over Mona Sur. Four composites were made up; Mona Sur A comprising beds A and B, Mona Sur B with beds C and D, Mona Ridge A with Bed ! and Mona Ridge B with Bed 2A. In addition Mona Sur samples 19011 from Bed A and 19029 from Bed D were tested.
A summary comparison of the test results is attached together with results recieved from Cimprogetti.
For those unfamiliar with Chilean limestones it should be noted there are no known high grade limestones with plus 98 per cent calcium carbonate available in the central region of Chile for the production of Burnt Lime. Producers make do with near 90 per cent calcium carbonate.
Three of the samples tested. Mona Ridge A, Mona Sur A and Mona Sur sample 19011 have 1.04, 5.71 and 10.82 per cent magnesium oxide. These all incur near the base of the 215 meter thick limestone formation. If desired the MgO content in the burnt lime produced can be modified by selective mining, blending or simply mining those beds with a minimum amount of MgO .
The Mona Ridge B sample shows much higher decrepitation at 950 and 1050 centigrade than the other five samples tested. This sample unlike the others has been bly recrystallized by an intrusive.
As mentioned above, carbon is present in all the high grade limestone and may reach as much as 5% in some sections. According to Penta Engineering, a company well versed in lime production, the presence of carbon does not affect the quality of lime produced if correct kiln procedures are followed. The carbon should reduce fuel consumption in the kiln and increase the percentage of free lime in the final product.
ACCESS FOR MINING OPERATIONS
The present access road to the base of the Mona Ridge limestone zone branches off from the road up the Maipo valley. From here, 6500 meters of road climbs to an altitude of 2790 meters with a gradient near 10%. There are five switchback curves in the last stretch, any one of which can be used to make near horizontal roads to provide access for adit based mining into the Mona Ridge high grade limestone. Access to develop and mine the South Mona high grade limestone can either be made by prolonging the 6500 meter road already mentioned for 3000 meters, or by making 7500 meters of new road, with an 8% per cent gradient, off the Codelco exploration road which runs up the east side of the Rio Blanco, immediately to the west.
The high grade limestone beds are entirely within lower grade limestone. Contacts are marked by a gradation, which, unlike sharp contacts, favours rock stability. This aspect, together with the near vertical attitude of the limestone suggests cheap sub level stoping will be feasible as a mining method. If widths of 70 meters do indeed occur, open pitting could be feasible in the early years (see attached “Catedral Lime Project” by John Selters).
A modern lime plant can meet the most stringent environmental requirements. The plant at Catedral would be constructed under close supervision of Penta Engineering, experts in lime and one of the leading companies in the field of process engineering related to cement and lime. Dames and Moore, a group specialising in environment matters in Chile and throughout the world, is confident requirements can be met for a 500 ton per day lime plant at Catedral.
This report was prepared by Dr. David Thomson, Executive Vice President and Director of Exploration of SAGC and a “qualified person” for the purpose of National Instrument 43-101.