Crespo project located in southern Peru, approximately 145 kilometres southwest of Cuzco and 587 kilometres southeast of Lima.
The project is one of a number of properties acquired by the Hochschild Mining in 2008 as part of the Liam JV/Southwestern Resources land package.
The Project is located on the western slopes of, and on the continental divide of the Cordillera Occidental (Western Cordillera) of the Peruvian Andes. The area is well above tree line in the Altiplano which is an undulating high altitude plain of gentle to moderate slopes with elevations ranging from a high 5,371 m on Cerro Crespo.
The Liam property was originally identified by Southwestern and staked based on a satellite image anomaly thought to represent hydrothermal alteration. Initial reconnaissance, 1:100,000 scale geological mapping and concurrent rock and stream sediment sampling were carried out by Minera Teck Peru S.A. on the original two Liam claims, Liam II and III (totaling 1,600 hectares) in May 1995. During the five-day helicopter-supported program a total of 24 rock samples were collected and a 4.5 by 2.0 km alteration zone of silicification and argillization was outlined. The geochemical analyses indicated low value precious metal anomalies with two samples returning greater than 100 ppb with a high of 167 ppb gold. Caeilles (1995) concluded that the Liam property hosted a low-sulphidation epithermal system and had a low priority. His recommendations were indecisive and inconclusive.
Also during 1995, Cominco carried out a brief first-pass program on their superimposed 1,000 hectare La Francia claim. Their mapping outlined high-sulphidation alteration, consisting of vuggy silica, alunite and advanced argillic alteration and a 450 metre by 350 metre breccia zone in the Cerro Crespo area. They collected a total of 101 samples comprising 47 rocks and 54 soils. Five rock samples were anomalous in gold with values up to one gram per tonne gold and two soil samples were anomalous in gold with values up to 1.9 g/t gold. The gold anomalies were coincident with anomalous silver and lead. The anomalous rock and soil samples were collected from the west side of Cerro Crespo, outside of the La Francia claim.
A second phase Minera Teck program consisting of 1:10,000 scale geological mapping and sampling was conducted in November 1996 with a total of 118 rock samples being collected. The program outlined five alteration zones (A-E) with zones “A” and “D” containing anomalous gold in rock values. Hydrothermal alteration consisted of silicification and argillization. Analyses of nine samples collected in Zone “A” returned gold values up to 553 ppb gold while analyses of four samples collected in zone “D” returned values up to 683 ppb gold. Both the zones contained coincident silver and epithermal indicator elements arsenic, antimony, bismuth and mercury as well as lead.
The June 1997, the Teck third phase program consisted of grid installation followed by 1:5,000 scale geological mapping with concurrent detailed grid rock and soil sampling and 33.25 line km of induced polarization (IP) and magnetic surveys on the Conejita grid. In October 1997, with the aid of a qualified mountain climber, detailed rock sampling was carried out over Cerro Crespo, where a total of 81 rock samples were collected. The grid work was concentrated over alteration and anomalous gold zones “A” and “D” (now labeled “A” and “B” respectively) where an additional 675 samples were collected (567 rocks and 27 soils).
Analyses of the 567 grid rock samples included 2 samples > 500 ppb gold, 14 samples > 200 ppb gold, 22 samples > 100 ppb gold, and 49 samples > 50 ppb gold. Almost all of the anomalous gold values were restricted to the two anomalous zones and all had coincident silver and epithermal indicator elements (arsenic, antimony, mercury and bismuth) as well as lead anomalies. Zone “A” consisted of three individual anomalous gold zones measuring 50 m to 500 m by 200 m to 400 m, 250 m by 50 m and 300 m by 100 m respectively. The entire zone averaged 72 ppb gold in 17 rock samples with a high of 142 ppb gold. Zone “B”, the largest gold zone, was 900 m by 400 m to 1,000 m and averaged 173 ppb gold in 39 rock chip and talus samples and was centred over Cerro Crespo with anomalous values exposed over a vertical extent of at least 150 m.
Geophysical surveys consisted of 12 line-km of IP (pole-dipole, a=50 m, n=1-6, time domain) on seven lines and 29.1 line-km of ground magnetics on 15 lines. The IP survey suggested a central zone of high resistivity (centred over Cerro Crespo and gold zone “B”). The magnetic survey showed a central part of the grid that suggested a possible deeprooted magnetic anomaly coincident with the central resistivity high. This central zone of high resistivity was flanked by zones of high chargeability, often with associated high resistivities.
Completed between September 4 and November 8, 1998, the 1998 drill program consisted of twelve HQ- and NQ-diameter diamond drill holes totaling 1,781.2 m.
Prior to commencement of the drilling, 19 km of access road was constructed from the existing main road north of Arcata to the drill camp adjacent to Cerro Crespo. An additional 14 km of drill access roads was constructed to drill sites.
Of the 1,781.2 m drilled, 1,637.8 m was HQ diameter core and 143.4 m was NQ diameter core. As two to three “up” holes were originally planned for Cerro Crespo (gold zone “B”), an underground LM75 rig was chosen due to its reported ability to drill “up-directed” holes. However, only one up-directed hole (hole LM98D02) was drilled and it was abandoned at a length of only 62.30 m.
A total of 747 core samples were collected during the 1998 drill program. All of the samples were pulverized by ALS Chemex Labs (“Chemex”) in Lima, Peru and the pulps sent to Chemex Labs in Vancouver, Canada to be analyzed for gold by fire assay and atomic absorption finish and silver, copper, lead, zinc, arsenic, molybdenum, bismuth and antimony by aqua regia digestion and ICP-AES (inductively coupled plasma-atomic emission spectrometry) finish. Mercury was analyzed by flameless atomic absorption spectroscopy. Gold and silver results were included in the respective drill logs. Anomalous gold (> 0.1 g/t gold) values and weighted average gold and silver drill intersections were plotted on sections. In order to determine epithermal alteration zoning, PIMA (portable infrared mineral analyzers) spectral analysis study was completed on holes 1B, 2, 3, 4, 5B, 6, 7 and 8. Core recovery was generally good, however, in some sections poor recovery was encountered.
After Teck decided not to contribute to the vigencia payments in June 2002, Misosa reviewed the results of the prior Liam Project work and concluded that it was still a target of merit and deserving of additional work. Consequently, Misosa carried out a detailed geological mapping and channel sampling program on the upper part of the Cerro Crespo butte from early September to early October 2003. A total of 325 channel samples ranging in length from 0.30 to 2.00 m were collected and the area was mapped at a scale of 1:500. From mid-May to early June 2003, Misosa completed the geological mapping of Cerro Crespo and collected an additional 85 samples from the south-southeast part of the butte.
Positive analytical results were received from the channel samples and in June 2003, Misosa commenced a drilling program consisting of 19 short diamond drill holes which totaled 3,197.55 m on Cerro Crespo.
On a regional basis, the Liam Gold-Silver Project is located in the central part of the northwest-trending Tertiary Volcanic Belt of southern Peru. The volcanic belt has been developed on top of older, mainly sedimentary, Paleozoic and Mesozoic units, which in general lie to the southwest and northeast of the volcanic belt. Northwest-trending, beltparallel zones of Cretaceous to Tertiary age felsic intrusives lie to the southwest and northeast of the central part of the Tertiary Volcanic Belt.
Dominant structural trends are northeast, northwest and to a lesser extent north-south. Base metal mineralization generally occurs associated with the intrusives as porphyry and a skarn-type mineralization. Gold-silver mineralization, usually of the high or low sulphidation epithermal type, tends to occur within a northwest-trending, belt-parallel zone, centrally located in the Tertiary Volcanic Belt. Examples are the Madrigal, Caylloma,
Suckuytan, Orcopampa, Poracota, Ares and Arcata mines and prospects to the south, and Santa Rose and Selene to the northwest of Liam.
Regional Geology, Depertment of Cusco, Peru.
Within the Liam Regional Venture Area, the oldest volcanic units are those of the Tacaza Formation which in turn are overlain by the Late Miocene Alpabamba volcanics consisting of bedded, felsic to andesitic tuffs and lavas and associated re-worked units. It is the Alpabamba units which host the Cerro Crespo-Queshca gold-silver mineralization. Following the formation of the Alpabamba units they were hydrothermally altered and mineralized. The Liam Core site is considered to have been a volcanic centre and the site of on-going cratering, brecciation, alteration and mineralization.
The generally unaltered andesitic Barroso Group volcanics of Pleistocene age were extruded over the argillically altered Alpabamba volcanics. Quaternary alluvial and glacial deposits occur throughout the lower areas and valleys. Local structural trends appear to duplicate those that are present on a regional basis. The Aluja zone of high-sulphidation type mineralization is hosted by the Barroso volcanics.
Cerro Crespo butte is a high-level, complex, hydrothermal vent system located on the southern side of the maar-like crater and exhibiting several felsic diatreme/brecciation events. At a depth of 150 to 200 m some of these diatreme/breccia zones become narrow, fault-controlled feeder zones. The original rock textures have been almost completely destroyed by the hydrothermal and phreatomagmatic processes with three types of breccias currently being recognized: a hydrothermal breccia, a phreatomagmatic breccia and a weakly brecciated, very strongly silicified unit. In all these units, silicification is pervasive, multi-episodic and associated with alunite.
Work by Misosa has indicated that the underlying units in the area are flow-banded rhyolites, lapilli tuffs and dacitic crystal tuffs of the Miocene Alpabamba Formation. Rhyodacites were reported in the deeper parts of some of the Teck drill holes at Cerro Crespo.
These units are considered to be localized in the central vent area of a large volcanic complex composed of one or more craters with an 800 m diameter maar-like crater flanked by Cerro Crespo to the south and the larger Queshca crater to the north. These features are considered to occur in the central part of an extensive zone of high sulphidation argillicsiliceous alteration.
On the lower southeast slope of Cerro Crespo are dacitic crystal tuffs intercalated with silica sinters and silicified ash flow tuffs and in places thin-bedded lacustrine sediments, which may have been deposited in small crater lakes. Lapilli tuffs have been mapped in contact with hydrothermal breccias in the northern, western and southwestern parts of Cerro Crespo and flow banded rhyolites occur on the northern end of Cerro Crespo. All
these units are moderately to strongly silicified and argillized. In places limonite after sulphides is present and most units are strongly oxidized. These units appear to be subhorizontal to north dipping (towards the maar-like crater). At Queshca, pyroclastic breccias and crystal tuffs dipping at low angles to the south (inwards) occur on the northern edge of the maar-like crater. Within the maar-like crater, thin-bedded crater-lake sediments and
intrusive breccias have been mapped.
Preliminary structural interpretations by Misosa indicate the presence of northeast, northsouth and northwest-trending structures. At Cerro Crespo, a set of east-west fault structures has been identified. These appear to generally have a left-handed displacement and to have produced five small fault blocks. These faults are syn-and post-mineralization and have controlled the emplacement of feeder structures and the breccia zones.
In summary, the Liam Core Zone area of mineralization is considered to be localized in a large volcanic complex consisting of several maar-like craters surrounded by sub-horizontal to inward dipping felsic volcaniclastics, flows and epiclastics which have been extensively faulted and fractured, pervasively silicified and argillized and intruded by multiple diatreme and hydrothermal breccias. Gold-silver mineralization appears to have been introduced in association with the introduction of the various breccia units.
Geology of the Liam Gold-Silver Property
The Liam Regional Venture Project mineralization discovered to date consists of three types:
- high sulphidation type epithermal gold-silver mineralization;
- low sulphidation type epithermal gold-silver mineralization;
- silver-lead-zinc mineralization in limestones.
The Soteco Joint Venture initially identified the Liam area as a zone of high sulphidation type epithermal gold-silver mineralization and in particular that the Cerro Crespo butte could represent a vent related diatreme-type body. Drilling at Cerro Crespo by Soteco was generally below the base of the butte (except for one, upward directed hole). The Soteco sampling showed that Cerro Crespo was anomalous in gold and silver; however, drilling marginal to and to some degree below Cerro Crespo produced only anomalous precious metal values.
Subsequently Misosa mapped and sampled in detail Cerro Crespo and Queshca and then carried out an initial diamond drilling program at Cerro Crespo. Detailed mapping and sampling in 2002 and 2003 resulted in the collection of 410 channel samples mainly on the top of Cerro Crespo and on its northern and eastern flanks. The mapping identified the various breccia units described above in Item 9, Liam Core Zone Geology, while the sampling identified five areas, from northwest to southeast and referred to as Areas A, B, C, D, and E, of gold-silver mineralization with grades ranging from anomalous to being of economic interest. Results of this mapping and sampling have been reported (Winter, 2003).
The Misosa channel sampling at Cerro Crespo produced the following conclusions:
1) Cerro Crespo is a high level, complex volcanic hydrothermal vent system within an extensive high sulphidation alteration zone.
2) A significant gold-silver zone of mineralization is associated with the hydrothermal vent system.
3) High grade silver values with subordinate gold were found in Zones A, B and C in the upper part of the butte at elevations between 5,350 and 5,375 m, and also in Zone D at an elevation of 5,200 m suggesting 150 to 175 m of vertical continuity in the eastern part of the butte. In Zone E at 5,150 m silver values decrease but
4) The upper part of Cerro Crespo is strongly oxidized, however, Misosa geologists consider that silver migration is generally in the order of centimetres.
In mid 2003, Misosa carried out two channel sampling programs at Queshca with the results being reported in press releases by Southwestern on September 23, 2003 and October 31, 2003 and summarized in Winter, 2003.
Queshca Zones 1 and 3 are at elevations between 5,125 and 5,150 m, while Zone 6 South is about 5,030 m, and Zone 6 North spans elevations from 4,950 to 5,000 m i.e. the lowest part of Zone 6 North is at least 175 m below Zones 1 and 3. It appears that the grade of the mineralization is increasing with depth in the stratigraphic sequence. The Queshca volcaniclastic units are dip south towards the maar crater. The distribution of the gold and silver values in this area may be related to the porosity and permeability of the volcaniclastic/epiclastic units in this sector and possibly the presence of more impermeable units, higher in the volcanic stratigraphy, which have produced a „cap rock‟.
A second sampling campaign was undertaken to check the high gold values reported in the earlier sampling. This sampling program of 303 samples included the sampling of trenches 20 m in length with individual channel samples being two m in length. The assay results from this second set of samples confirmed the values obtained in the first sampling campaign.
In June 2003 Misosa commenced a drill program at Cerro Crespo, which resulted in 19 holes totaling 3,197.55 m being completed. The gold and silver values as reported in press releases by Southwestern are summarized in Winter, 2003.
From the mapping at Cerro Crespo as well as the diamond drilling, it is possible that the gold-silver mineralization at Cerro Crespo is confined to the brecciated and highly silicified zone of the butte, which is in turn surrounded by an argillic-siliceous alteration zone. The mineralized zone trends northwesterly, with a strike length in the order of 350 m, a width of 125 to 150 m and a vertical extent of approximately 150 m. The zone of better grade mineralization appears to be “V” shaped in cross-section with the zone being wider at the top of the butte and diminishing in width at depth as it passes into the feeder zones. The main areas of mineralization are on the two arms of the “V” with smaller, discontinuous areas within the upper mouth of the “V”. This overall picture is distorted by the east-west faults and movement of the adjacent blocks.
Source: Annual results 2018 Hochschild mining 2018; Independent technical report Liam Gold Southwestern Resources Corp. by Caracle Creek International Consulting Inc., 2008.