Golden opportunity Limão Gold Property, Brazil
Summary
The Limão project is situated in the Tapajós Gold Province in Central Brazil and consists of several exploration licences totaling 11,500 hectares. An additional 7,000 hectares has recently been optioned to the Company. The Tapajós region is one of the primary alluvial gold sites in Brazil. The Tapajós became a significant producer in the 1980s by a flood of small scale alluvial miners called garimpeiros. Peak gold production in the region occurred in the late 1980's with as many as 500,000 garimpeiros. Real production numbers are unknown but estimates range from 20 to 30M ounces of gold.
Property History
Between 1987 and 1990, a Brazilian company carried out systematic prospecting and exploration work in the area which included geochemical and geophysical surveys followed by a small drill program. Their work focused on the Limão Pit that was previously exploited by artisanal gold miners. Holes drilled under the Pit returned promising results such as 47 g/t Au over 13 metres and 18.7 g/t Au over 6.8 metres. The location of these holes is uncertain. The Pit has since been filled with water.
During 1994 Barrick Gold conducted a data review of the area and carried out a preliminary geological and geochemical reconnaissance program that resulted in a geochemical anomaly around the Limão Pit. In 1995, Barrick employed a consultancy to operate the project and exploration work continued on a local and regional scale. The 1995 program consisted of geological mapping, gridded soil sampling, and ground geophysics. This program further defined the gold anomaly around the Limão Pit, as well as, defining several gold anomalies along their exploration grids. Recommendations from the work included a small drill program, which was not carried out.
Fifteen surface rock samples collected by Barrick returned values ranging from 1.75 g/t to 25 g/t gold hosted in pyritized syenite to syenogranite. Barrick further reported that gold mineralization in the area was directly associated with a syeno-granitic body rich in pink K-feldspar.
At the Limao pit, Amerix's drilling has intercepted gold mineralization occurring in potassic- and hematite-altered, syenitic intrusive rocks that are strongly mineralized with pyrite. These syenites show little deformational fabric, and the pyrite occurs in disseminations, clots and along fractures. The style of gold mineralization can be seen in drill core photos that are posted at the Company's website for each drill hole.
Location and Access
The Limão Project is located in the north-central portion of the Tapajós Gold Province, approximately 180 kilometres south of the city of Itaituba, and 30 kilometres north-east of Cuiu-Cuiu, the oldest and most important prospecting community in the region. Access to the property is exclusively by air from Itaituba which has a population of 70,000.
2012 08 28 Limao Google Earth
Regional and Property Geology
The Limão Project is located in the Amazon Craton, in the Central Amazon sub-province. It is composed of the Cuiu-Cuiu Metamorphic Suite that represents the undivided basement formed by migmatized gneisses, granitoids of varied compositions, relics of amphibolites, rock of granulite facies, and remains of the volcanic-sedimentary Jacareacanga Group.
During the mid-Paleoproterozoic the area was influenced by a widespread magmatic-volcanic event and sedimentation represented by the Uatumã Supergroup. This is further divided into two major units; the basal unit called the Iriri Formation, composed of acidic volcanics rocks, associated tuffs and sediments and intrusive Maloquinha Suite represented by acidic intrusive rocks. The Maloquinha Granite is hosted preferentially in epizonal crustal portions, exhibiting alkaline metaluminous characteristics and probably is responsible for the formation of prospective sites for gold mineralization.
In the Cenozoic (Ma), deep tropical weathering resulted in the oxidization of the rocks and formed the present day drainage and landscape.
Regional Deposits and Resources
The Limão Property is situated along the NW-SE Tocantinzinho Trend. This trend hosts notable gold properties such as Eldorado's Tocantinzinho Property (2.5M oz) and Magellan Mineral's Cuiu-Cuiu Property (1.3M oz). The Limão Property is located on the northern portion of the trend and exploration by Amerix shows that the gold mineralization at the Limão Pit is associated with pyritized and potassic altered syenitic or alkalic rocks. Gold deposits clearly linked to alkaline magmatic rocks host many gold deposits in the Abitibi Greenstone Belt such as the Malarctic Deposit and the Young Davidson Deposit.
2012 Drill Program
In May of 2012, the Company began a drilling program designed to follow up its earlier exploration programs. Those earlier programs provided property wide airborne magnetic and radiometric surveying and four grids of detailed soil geochemical auger sampling, mapping and rock sampling.
Limão Pit Geochemical Survey Results(Click for Full Size PDF)
Limão Pit Drill Hole Plan(Click for Full Size PDF)
2012 Limão Pit Drill Results
Diamond drilling is accompanied by a quality assurance and quality control program that is managed by Amerix's geologists and includes industry standard documentation during data collection, reporting, and down hole azimuth and angle surveys. Drill core sample intervals were selected based on geological and mineralogical changes in the rock and averaged near 1 metre sample length within mineralized intervals and the immediate wall rock using sample lengths that ranged from a minimum of 0.5 metres to a maximum of 1.5 metres. NTW size rock drill core was split in half using a diamond saw preserving half of the split core for reference and half to be sent for gold analysis. Standard references, blanks, and quartered drill core duplicates were also inserted into the sample stream prior to transport. All samples were delivered to Acme Laboratories preparation facility in Itaituba, Brazil where the samples were crushed, pulverized, split, and shipped to Acme's Santiago, Chile laboratory for fire assay gold on a 30 gram split. Samples analyzing greater than 10 grams per tonne gold, or over the fire assay detection limit, were automatically re-analyzed for gold by gravimetric gold analysis. Both Acme Itaituba and Acme Santiago are registered under International Standards Organization's ISO 9001:2008 quality control program. The Company utilizes a chain of custody program overseen by its geologists concerning sample transport from the Limão property to Acme's Itaituba preparation facility.
Amerix Historical Exploration Work
The Company's review of the area consisted initially of satellite/aerial photography and location of the artisanal workings. In 2009 a crew was mobilized to the property and re-established the camp and airstrip. Initially a small grid was established for sampling and mapping control over the pit area and other artisanal workings. A total of 11 float samples were taken from sulphide-rich syeno-granitic rocks located in the pit area. Results range from 2.37 g/t Au to 106.6 g/t Au with an average of 38.5 g/t Au or 1.12 oz/t Au. Sample results from the syeno-granitic rocks are summarized in the following table.
The Company believes these samples to be representative of bedrock mineralization at the bottom of the open pit which was previously mined by local miners. The open pit is now filled with water and is believed to have been up to 20 metres deep.
In 2009 and 2010 a total of 1841 one-metre auger samples were taken at 20 metre intervals along parallel north-south lines spaced at 100 metre intervals. Sample results from the 2009 and 2010 geochemical surveys located several gold in-soil anomalies and reconfirmed previous operator's results. Three grids (North, Central and South) were established for sampling and mapping control. Sampling defined a strong east-to-west anomaly on the central grid measuring 1,300 metres long. The pit area is located 200 metres north of gold-in-soil anomaly. The northern grid defined several gold-in-soil anomalies. The most notable anomaly covers an area of 300 by 200 metres located approximately 400 metres north-northwest of the open pit area. The Southern grid covers an area of 0.45 square kilometres and a 200-by-200 metre gold-in-soil anomaly was defined approximately 1500 metres south of the historic drilling. Visible gold was observed in the quartz veins in this area and rock sample results returned high grade gold values. An NI 43-101 Technical Report was prepared in May 2011 to summarize all work completed to that date and is filed at SEDAR and can be accessed below at the end of the section.
Property & Grid Work - Location Map (Click for Full Size PDF)
Central Grid, Limão Pit Area
During late 2011, the Company established a 10 metre by 10 metre spaced and a 20 metre by 10 metre spaced, infill soil grid, as a continuation of its earlier, 100 metre by 20 metre spaced soil grid. These grids cover the Limão Pit area that is the main gold target at the Central Grid. The Limão Pit target is characterized by pyrite bearing syenite that was exploited by small-scale artisanal miners and diamond drilled during the 1980's using conventional drilling methods. The interpreted NW strike of mineralization from the historic drilling, combined with mapping by the Company's geologists, guided the orientation of the infill soil grid and a total of one thousand four hundred and sixty eight, 1-metre manual soil auger samples were collected along a northwest trend. The infill grid is bisected by two creeks that were subject to alluvial placer mining. The figure below shows the soil sample locations.
Central Grid Geochemical Survey Results (Click for Full Size PDF)
The 1-metre soil auger samples were collected from a regolith consisting of colluvium, laterite, saprolite, alluvium, and tailings that included placer mining reject and tailings from the Limão Pit. Excluding alluvium and tailings material, soil assay results from colluvial to saprolitic material have defined a 600 metre northwest trending gold in soil anomaly defined by subtle, sporadic clusters of soil anomalies ranging from 25 to 1,217 parts per billion gold and represent the majority of the soil samples collected. Apart from the colluvium, laterite, and saprolite, alluvial and tailings samples returned results ranging from 11 to 6,660 parts per billion gold with one outlier of 12,900 parts per billion gold.
All soil samples from the project were delivered to Acme Labs preparation facility in Itaituba, Brazil where the samples were dried, sieved, split, and shipped to Acme's Santiago, Chile laboratory for gold analysis by fire assay with atomic absorption finish on a 30 or 50 gram split. Acme Laboratories is registered under International Standards Organization ISO 9001:2008 quality control program. The Company utilizes a QA/QC chain of custody program overseen by its geologists concerning its samples.
South Grid Workings: Geochemical Survey, Rock Sample Compilation, Location and Results
The South Grid covers 0.6 square kilometres and was established primarily to cover an area of past, small scale, artisanal mining. Company geologists have identified quartz veining occurring along easterly to westerly oriented, sheared contacts within predominantly granitic host rocks as exposed in a shaft and a cut face at the workings. A second gold in soil anomaly occurs in the east section of this grid area. This anomaly extends for approximately 250 metres in an easterly to westerly direction and is open to the east. The South Grid geochemical gold anomaly is characterized by a greater than 20 ppb gold in soil anomaly, traceable for 350 meters along a 290 degree trend, and that is coincident with abandoned, small scale mine workings that exploited gold mineralization hosted in shears with quartz veins. Limited mapping completed in the area of the workings has identified an easterly striking, near vertical shear occurring at or near the contacts of quartz diorite, diabase, and granite with wall rock alteration consisting of silicification plus-or minus muscovite. The artisinal mine workings including an open cut, shafts, and drifts coincide with 150 metres of interpreted strike along the shear. During the 2010 and 2011 exploration campaigns, a total of 60 rock samples were collected from the South Grid artisanal workings in the form of chips, channels, and grab’s from the open cut, shafts, drifts, and test shafts in both saprolite and unweathered rock. Visible gold was noted at several locations in oxidized quartz veins. In fresh samples gold is associated with pyrite and chalcopyrite. It should be noted that most of the Limão Gold Property is covered by deep weathering and layers of colluvium, alluvium and saprolite with limited surface rock outcropping.
South Grid Geochemical Survey Results (Click for Full Size PDF)
Of the 60 rock samples collected, nine chip and channel samples and one panel sample were taken from the shear, veins, and wall rock in both saprolite and fresh rock at 3 separate locations within 88 metres along the conjectured strike of the shear. Those samples were collected along the face of the open cut, a drift into the face of the cut, and a drift worked from a shaft to 28 metres below surface and returned assay values between 0.058 and 275.0 grams per tonne gold or 0.002 to 8.84 ounces per tonne. The estimated true width of the shear is 1.0 to 2.1 metres and it contains singular to multiple quartz veins that range in thickness between 0.05 to 0.4 metres. Quartz veins are hosted in the mineralized shear and weakly mineralized wall rock. Within the shear there is a strong correlation between quartz vein and anomalous gold content. The results of those samples are presented in the Figure that follows.
South Grid Diamond Drill Hole Locations (Click for Full Size PDF)
Amerix drilled 4 holes in 2012, LDHM-06 to 09 drilled on 3 north-south drill sections spaced 125 and 60 metres apart from west to east. LDHM–06 intersected 7.36 grams gold per tonne over 1 metre from 78.9 metres to 79.9 metres and LDHM–09 intersected 39.4 grams gold per tonne over 0.5 metres from 53 metres to 53.5 metres. These are encouraging results as a preliminary test of this second style of gold mineralization occurring at the property. These drill holes have only tested a portion of the gold in soil geochemical anomaly at the South Grid. These veins are interpreted to be "pinch and swell" style quartz veins that host high grade gold mineralization. This concurs with the experience of the artisan miners (garimpeiros) that previously opened workings along these veins. Company geologists were able to access adits and view the veins occurring in saprolite and rock near surface. Photos follow:
South Grid Quartz Veining in Garimpeiro Workings
South Grid Quartz Veining in Garimpeiro Workings
.jpg)
Subbão Grid, Au (ppb) in Soil Results
The Subbão soil grid covers an area of 116 hectares and was established over small scale artisanal mine workings, called the Subbão Zone, where saprolite and rock samples had returned anomalous gold assay results mainly from grabs, selective grabs, and stockpiled crusher waste that ranged from <0.005 grams per tonne gold to 361.5 grams per tonne gold. Higher grade samples resulted from hand selective grabs of fine quartz vein material where visible gold was occasionally noted. Gold values are expected to have been enhanced by oxidation of sulphide bearing, fine quartz veins. Limited exposure of saprolite outcrop and evidence gathered from saprolite in shaft dump piles show fine, less than 5 centimetre thick, quartz vein or veins hosted in and along granite, a fine grained volcanic, and a fine mylonite with some sericite and fracture chlorite in wall rocks. The contact between granite and the fine grained volcanic is speculated to be a structural focus for quartz veining and shearing.
In total, 775 one-metre manual soil auger samples were collected at twenty metre stations along 16, one hundred-metre spaced wing lines and 1 baseline at the Subbão Grid. This grid was also established to explore west-northwest trending regional structures identified from satellite images and an airborne magnetic survey, as well as, possible secondary structures. In the vicinity of the artisanal workings, soil assay results show a localized gold anomaly that requires follow up with detail, infill geochemical sampling and mapping to define the limits of the mineralization encountered at the Subbão Zone. Sparse localized colluvial and saprolite gold in soil anomalies were also encountered elsewhere in the Subbão soil grid, occasionally near abandoned, small scale alluvial/placer operations.
Photo Gallery
To view project area photos please click here.
Project Info
To view related technical publications click on the links below:
Syenite –Associated Disseminated Gold Deposits in the Abitibi Greenstone Belt
https://rd.springer.com/article/10.1007/s001260100186
Gold Deposits: Tapajós and Alta Floresta Domains
https://rd.springer.com/article/10.1007/s001260100172
Granite-Related Paleoproterozoic, Serrinha Gold deposit
https://geol.queensu.ca/isotope_lab/pdfs/Moura et al 2006.pdf