TSX:RMX | NYSE AMEX:RBY March 31, 2011
TORONTO, March 31 /CNW/ - Rubicon Minerals Corporation (RMX: TSX) (NYSE-AMEX: RBY) (the "Company" or "Rubicon") announced amended inferred mineral resource and geological potential estimates today for its Phoenix Gold Project, F2 Gold System. The amended estimates are a result of the previously announced review by the British Columbia Securities Commission of the Company's NI 43-101 technical report filed on January 11, 2011 (the "Report").
The following amended estimates were prepared by Peter George of Geoex Limited, the Company's independent QP and author of the Report (the "Author"), and are effective March 31, 2011:
1. Amended Inferred Mineral Resource Estimate
Polygonal Model Inferred Mineral Resource Estimate - Uncapped and Capped
Polygonal Model Inferred Mineral Resource Estimate
(5 g/t gold cut-off and 10 gram x metre product (core length) - surface to 1200 metres below surface) |
| Inferred Tonnes | Gold (Uncapped Grade) | 10-5-2 oz Capped Gold Grade* |
Inferred gold grade
(g/t) | Inferred
Ounces | Inferred gold grade
(g/t) | Inferred
Ounces |
| 5,500,000 | 20.34 | 3,597,000 | 17.29 | 3,057,000 |
The polygonal model inferred resource estimate is based on composites which satisfy a 5 g/t gold cut-off and 10 gram x metre product (core length) as at July 31, 2010.
The estimates are in-situ and undiluted and figures are rounded.
*10-5-2 refers to an empirical capping strategy that caps gold values greater than 10 oz/ton to 10 oz/ton (342.8g/t), those between 5 and 10 oz/ton to 5 oz/ton (171.4 g/t), those between 2 and 5 oz/ton to 2 oz/ton (68.6 g/t). Values less than 2oz/ton remain uncapped.
The polygonal model inferred mineral resource estimate prepared by the Author was based on 166,886 metres of diamond drilling in 237 drill holes carried out between February 27, 2008 (the date of the initial discovery) and July 31, 2010. The above inferred mineral resource estimate was prepared using the polygonal calculation method (see "Resource Calculation Methodology" below for details) which, in the opinion of the Author, is the appropriate method and is typically used for this type of deposit. The cut-off used is considered to be an economically reasonable estimate of breakeven mining costs.
Inferred resources are too speculative to have economic consideration applied to them and there is no certainty that the inferred resources will be converted to measured and indicated resources.
2. Amended Block Model Validation Inferred Mineral Resource Estimate
In addition to the polygonal model mineral resource calculation, as a means of validating the inferred mineral resource estimate by an independent method, a block model was calculated utilizing Surpac software.
Block Model Validation Inferred Mineral Resource Estimate (5 g/t cut-off) (surface to 1200 metres below surface)
Inferred
Tonnes | Uncapped block
model estimate | 10-5-2 oz Capped block
model estimate* |
Inferred gold
grade (g/t) | Inferred Ounces | Inferred gold
grade (g/t) | Inferred
Ounces |
| 6,017,000 | 16.49 | 3,190,000 | 15.69 | 3,035,000 |
The block model inferred mineral resource estimate is based on composites which satisfy a 5 g/t gold cut-off as at July 31, 2010.
The estimates are in-situ and undiluted and figures are rounded.
*10-5-2 refers to an empirical capping strategy that caps gold values greater than 10 oz/ton to 10 oz/ton, those between 5 and 10 oz/ton to 5 oz/ton, those between 2 and 5 oz/ton to 2 oz/ton. Values less than 2oz/ton remain uncapped.
The block model inferred mineral resource estimate prepared by the Author was based on 166,886 metres of diamond drilling in 237 drill holes carried out between February 27, 2008 (the date of the initial discovery) and July 31, 2010. The cut-off used is considered to be an economically reasonable estimate of breakeven mining costs.
Inferred resources are too speculative to have economic consideration applied to them and there is no certainty that the inferred resources will be converted to measured and indicated resources.
Parameters selected for the block model validation inferred mineral resource estimate are detailed below under "Resource Calculation Methodology". On an uncapped basis, the block model estimates are within 9.4% of the tonnage, 18.9% of the grade and 11.3% of the total contained ounces of the uncapped polygonal estimate. On a capped basis, the block model estimates are within 9.4% of the tonnage, 9.3% of the grade and 0.7% of the total contained ounces of the capped polygonal estimate. While the Author does not consider the block model the most appropriate method for this type of deposit, the results provide strong supporting validation for the preferred polygonal estimate reported above. Capping has been carried out to allow an evaluation of the effect of capping. As additional data becomes available, additional studies of statistically based capping may be required.
3. Amended Geological Potential
In addition to the above referenced inferred mineral resource estimates, the Author carried out a re-evaluation of geological potential between 0 and 1500 metres below surface, based on an analysis of the distribution of current drilling (strike length of 898 metres as of July 31, 2010) and opportunity for infill and expansion drilling to depth. The system remains open along strike and to depth beyond the current limit of drilling.
The geological potential is based on the projection and extrapolation of the inferred resource present between 0 to 500 metres below surface as this area has the highest drill density of one drill hole per 55 m2 and contains an inferred resource of 2,988,000 tonnes grading 26.55 g/t gold containing 2,550,000 ounces of gold. In a portion of the area between 500 and 1500 metres below surface, drilling density is lower but still sufficient to qualify resources where drilling has been carried out. In the opinion of the Author, based on a review of project data, experience from elsewhere in Red Lake and general observations on lode gold deposits, the grade and tonnage profile of the area above 500 metres is likely to be replicated to depth with additional drilling. The Author estimates exclusive of the inferred resources, geological potential on a uncapped basis of between 1,670,000 and 4,360,000 tonnes grading 21.2 to 29.2 g/t gold for an additional 1,300,000 to 5,600,000 ounces of gold. If the 10-5-2 capping described above were applied, these estimates of potential would be reduced to 800,000 to 4,300,000 ounces of gold grading between 16.9 g/t and 23.2 g/t gold. A 10% upside and 20% downside potential for both tonnes and grade has been incorporated to address the possible uncertainty of the geological potential estimate.
The potential tonnages, grades and ounces set forth in the analysis of geological potential are conceptual in nature, as there has been insufficient exploration to define a mineral resource and it is uncertain if further exploration will result in the target being delineated as a mineral resource. Potential estimates are separate from the inferred mineral resources stated above.
The final amended NI 43-101 compliant technical report containing the amended inferred mineral resource and geological potential estimates will be filed on SEDAR within 14 days.
The principal differences between the amended estimates and those contained in the Report are as follows:
| (1) | The polygonal inferred mineral resource estimate was revised to include resources between 0 and 1200 metres below surface (originally 0 to 1500 metres). Changes are tabulated below: |
| |
| | Amended Polygonal Inferred Mineral Resource Estimate, March 31, 2011 |
| Uncapped (0 -1200 metres below surface) | 10-5-2 Capped (0-1200 metres below surface) |
| Tonnes | Au g/t | Ounces | Tonnes | Au g/t | Ounces |
| 5,500,000 | 20.34 | 3,597,000 | 5,500,000 | 17.29 | 3,057,000 |
Initial Polygonal Inferred Mineral Resource Estimate, January 11, 2011 Technical Report
| Uncapped (0 -1500 metres below surface) |
| Tonnes | Au g/t | Ounces |
| 6,204,000 | 20.1 | 4,007,400 |
Difference in Estimates
| Uncapped (Initial vs. Amended) |
| Tonnes | Au g/t | Ounces |
| 703,000 | 0.24 | 410,000 |
| (2) | Block Model estimates were revised to reflect estimates between 0 and 1200 metres below surface (originally 0-1500 metres below surface) and capping was applied. Changes are tabulated below: |
| |
| | Amended Block Model Validation Inferred Mineral Resource Estimate |
| Uncapped (0 - 1200 metres) | 10-5-2 Capped (0 - 1200 metres) |
| Tonnes | Au g/t | Ounces | Tonnes | Au g/t | Ounces |
| 6,017,000 | 16.49 | 3,190,000 | 6,017,000 | 15.69 | 3,035,000 |
| | | Initial Block Model Validation Inferred Mineral Resource Estimate |
| Uncapped (0 -1500 metres below surface) |
| Tonnes | Au g/t | Ounces |
| 5,830,000 | 17.17 | 3,210,000 |
| Uncapped (Initial vs. Amended) |
| Tonnes | Au g/t | Ounces |
| 187,000 | 0.68 | 19,700 |
| (3) | Geological Potential is now limited to between 0 and 1500 metres below surface (previously 0 - 2500 metres below surface) and results in the changes described above under "Amended Geological Potential". |
| | |
| (4) | The Author has clarified his reliance on the 5 g/t gold cut-off and has removed tables in the Report regarding a 3 g/t gold cut-off resource estimate. |
| | |
| (5) | The Author has removed certain polygons which are below 1.2 metre horizontal width although most of these are close to other data points that could justify inclusion with some additional drilling. This results in a reduction in tonnes of 8.1%, grade increases by 4.5% and total ounces decrease by 4.0% compared to the initial statement of uncapped polygonal inferred resource estimate. |
David Adamson, President and CEO of Rubicon, stated: "We appreciate the input the British Columbia Securities Commission has provided and especially wish to thank our shareholders for their patience and support during this period. All of us on the Rubicon team are pleased that the amended estimates confirm the fundamental and material nature, aspects and integrity of the mineral resource and look forward to moving the Project forward."
Resource Calculation Methodology
The construction of the polygonal and block models was a product of collaboration between Rubicon and Geoex. Rubicon personnel included Matt Wunder P.Geo, V.P. Exploration and Eric Hinton P.Eng., Project Manager. All data in the resource evaluation were reviewed by Geoex with Mr. Peter George of Geoex assuming responsibility for the resource and geological potential estimates upon which the statements reported herein are based.
Polygonal Resource calculation
Geological sections and plans at scales of 1:1000, 1:500 and 1:200 were reviewed by the Author. These plans and sections included a set of geological sections that were generated and interpreted by an independent geological consultant. Sections were selected at a tight spacing of 20 metres through the F2 Gold System and were based on all available geological and assay information. They show that major rock types can be correlated on section to depths of 1500 metres and over a strike length of approximately 1200 metres. The Author reviewed selected drill core from the F2 Gold System, reviewed geological logging and sampling protocols used by project staff and agrees with the geological interpretation derived from the geological sections. Gold mineralization ranging from low (>1 g/t) to high grade is observed within (i.e. is bounded by) major mapped geological units. As described above, the geological sequence is sub-vertical to steep west dipping.
The QAQC protocols of the Company have been independently reviewed and approved by a third party consultant. The Company also had an independent third party consultant audit the composite calculations. The Author is of the opinion that the database underlying the Geoex resource estimates is suitable.
The Author prepared both 3g/t and 5g/t assay composites tables in 3D AutoCad to allow inspection of the distribution of significant gold mineralized intervals excluding a large number (>4000) lower grade intercepts (>1 g/t gold). Significant drill intersections within bounding geological units and mineralized sub-zones were observed to conform closely to bounding geological units and are largely aligned in the direction of the East Bay Deformation Zone ("EBDZ"), i.e. they display a northeast trend and sub-vertical to steep westerly dip.
The Author has selected an elliptical area of influence with a minor axis radius of 37.5 metres and a major axis radius of 75 metres with the major axis plunging steeply to the south parallel to the local and regional structural plunge. The dimensions reflect distances that are well within the observed horizontal and vertical dimensions and continuity of the known mineralization.
The area of each polygon was determined in 3D AutoCad. The horizontal width of the polygon perpendicular to the plane of the intersection was calculated in the resource spreadsheet based upon the core width, the dip and azimuth of the hole at the long section pierce point and the strike direction of the long section. The volume of the polygon was determined by multiplying the area from the vertical section by the horizontal width at the pierce point on the long section. Tonnage is calculated by multiplying the volume of the polygon (cubic metres) by the average specific gravity (2.85 assumed for this amended resource estimate). Average grade is estimated by the weighted average of the sum of the polygon tonnes x grade divided by the total tonnes.
Block Model calculation
In order to validate the polygonal model, the Author reviewed the results of a second inferred mineral resource estimate derived using block model analysis. The block model was prepared using Surpac Version 6.1.4 software as follows:
The block model estimation was performed using the same data set used for the polygonal resource estimate. Drill hole assay data were reviewed and a composite interval of 1.0 metre was selected for the data set. During the compositing process, Surpac software declustered the data to address uneven spatial assay distribution. Variogram analysis was performed and block size optimization was carried out. Verification of Surpac block model assumptions, variogram analysis and input parameters was carried out by an independent third party.
The results of the variogram analysis are as follows:
| | | | | |
Variogram parameters
• Major axis (dip direction - near vertical): | | | | 36.0m radius |
| | | | | |
Anisotropy Ratios
• Semi major axis (strike direction): | | | | 1.40 (ratio to major axis) or 25.7m radius |
| • Minor axis (across strike direction): | | | | 3.40 (ratio to major axis) or 10.6m radius |
| | | | | |
Search ellipse parameters
• First Axis (strike direction): | | | | 13.40 degrees (Mine Grid)* |
| • Second Axis (plunge direction): | | | | 69.00 degrees |
| • Third Axis (dip direction): | | | | 10.00 degrees |
| • Inferred resource estimate used search parameters of 2 times variogram ranges |
| • Max search distance of major axis: | | | | 72.000 metres |
*Mine Grid zero degrees azimuth = 45 degrees clockwise rotation to magnetic North.
The variogram results are generally consistent with the geological model used in the polygonal estimation having two axes that approximate the observed geological and mineralized trend of the EBDZ (northeast). The plunge of the second axis is also generally consistent with the observed plunge in the geological model (70-80 degrees) used in the polygonal estimate.
Block Model Validation Inferred Mineral Resource
The block size selected for the block model was based on a block size optimization analysis performed using Surpac. The search method selected was inverse distance squared. The search radius employed was two times the variogram ranges (72 x 51 x 21 metres) and is consistent with standard block model methodology for inferred mineral resources. A minimum of three samples and maximum of five samples were selected as requirements for populating each block.
It is noted that the standard 2x variogram search parameter dimensions used to classify the block model inferred resource are larger than the polygons used in the polygonal estimate derived from analysis of sectional data which lends independent support to the polygon size selected in the polygon model which was derived independently from analysis of sectional geological and assay data.
The block model was constrained utilizing surfaces for the following:
- The lake bottom;
- The claim boundary; and
- The hanging wall geological contact to the F2 system.
The Author evaluated the effect of using the smaller polygonal search ellipse instead of the the 2 times variogram range which resulted in no material difference to the stated block model inferred mineral resource estimate.
RUBICON MINERALS CORPORATION
"David W. Adamson"
President & CEO