New Pacific Metals Corp. reported the preliminary metallurgical testwork results of the five variability samples from its Carangas Silver-Gold Project in OruroDepartment, Bolivia. This ongoing metallurgical testwork program consists of scoping-level cyanide leach and flotation testing and is carried out by Bureau Veritas's Metallurgical Division in Richmond, British Columbia, Canada.  Mineralized materials sampled from rejects of selected Carangas drill cores with assays were composited to five samples based on the type of mineralization and degree of oxidization.

 Host rock sample is altered volcanoclastic rocks of dacitic-rhyolitic composition. Cyanide leach tests for the fresh gold samples for the sample with less than 1% sulfur content have achieved 98.8% gold recovery and the second gold sample with approximately 3% sulfur content achieved 98.5% gold recovery.  The near surface, overlying oxidized, oxidized to semi-oxidized, and fresh silver-lead-zinc samples were tested with cyanide leaching and flotation. The cyanide leach tests achieved silver recoveries of 84.1%, 85% and 74.3%, respectively.   Whole ore flotation tests achieved silver recoveries of 72-77%, 90-94% and 99%, respectively.

Flotation tests for oxidized to semi oxidized samples also achieved zinc recoveries of 93-95%. Furthermore, 98-99% lead and 96-97% zinc flotation recoveries were achieved for the fresh silver-lead-zinc sample. These preliminary test results clearly demonstrate that high recovery rates can be expected for gold using cyanide leaching and for silver, lead, and zinc through conventional cyanide leaching and flotation for silver-lead-zinc mineralized materials.

Sample 1 was an oxidized composite silver-lead sample consisting of drill core rejects from shallow depth (25-66 m) with head grades of 183 g/t silver and 1.20% lead. Zinc content was negligible. The majority of the lead was present in an oxidized form. Initial whole ore cyanide leach testing showed that silver dissolved rapidly in cyanide solution with 84.1% silver recovery.

Further cyanide leach tests along with gravity concentration will be carried out to improve silver recovery. Early flotation testing indicated that silver recov ery during rougher flotation was modest in the 72-77% range, and lead recovery was very poor. Further improvement work is in progress.

Sample 2 was an oxidized to semi-oxidized composite silver-lead-zinc sample consisting of core rejects from shallow depth (9-46 m) with head grades of 106 g/t silver, 0.86% lead and 0.47% zinc. A portion of the lead was present in an oxidized form. Silver in this sample also dissolved rapidly in cyanide solution, and silver recovery was 85.0% based on a single cyanide leach test.  Silver recovery is expected to improve further with additional cyanide leach testing. Sequential selective flotation was applied to Sample 2 to produce a silver/lead concentrate and a zinc concentrate.

Initial flotation testing demonstrated promising recoveries for silver (90-94%) and for zinc (93-95%) into the combined silver/lead and zinc rougher concentrates. Lead recovery was relatively poor due to partially oxidized lead minerals. Based on what has been learned from Sample 1, lead recovery of Sample 2 is expected to increase considerably when the same approaches are applied.

Sample 3 was a fresh composite silver-lead-zinc sample consisting of core rejects from 110-172 m depths withhead grades of 151 g/t silver, 0.85% lead and 1.28% zinc. Oxidation has not occurred in this sample. Silver in Sample 3 dissolved very slowly in cyanide solution. After 72 hours, silver dissolution was still incomplete. Silver recovery was only 74.3% based on a single cyanide leach test.

A number of options are available to increase silver recovery and will be explored in future testwork As with Sample 2, sequential selective flotation was applied to Sample 3 to produce separate silver/lead and zinc concentrates. Initial flotation testing showed excellent flotation performance for silver, lead and zinc. When silver/lead concentrate and zinc concentrate are combined, total recoveries were 99% for silver, 98-99% for lead and 96-97% for zinc.  Sample 4 was a fresh composite gold sample consisting of core rejects with low sulfur content from 425-754 m depths and a head grade of 2.5 g/t gold and 0.62% sulfur. Contents of silver, lead and zinc were very low.

Preliminary cyanide leach testing demonstrated exceptionally high gold recoveries in a range of 98.2-99.2%.  Gold recovery was very robust and dropped only by 1.0% after grind size was coarsened from 80% passing 50 µm to 80% passing 150 µm, and cyanide concentration was reduced from 1.0 g/L NaCN to 0.50 g/L NaCN and oxygen sparging was replaced with air sparging. Sample 4 did not show any preg-robbing issue. Sample 5 was a fresh composite gold sample consisting of core rejects with high sulfur content from 430-746 m depths and a head grade of 3.88 g/t gold and 3.07% sulfur.

Contents of silver, lead and zinc were also insignificant. As with Sample 4, exceptionally high gold recoveries (97.2-99.0%) were achieved from initial cyanide leach tests. Gold recovery dropped only by 1.8% after grind size was coarsened from 80% passing 50 µm to 80% passing 150 µm, cyanide concentration was reduced from 1.0 g/L NaCN to 0.50 g/L NaCN and oxygen sparging was replaced with air sparging.

Sample 5 also did not show any preg-robbing issue.