Four main styles of base metal mineralization have been identified on the Property:
• Hydrothermal Quartz Veins (MQV);
• Stockwork (STK);
• Stratabound (SMS); and
• Mississippi Valley type (MVT).

MQV Mineralization
Vein-type mineralization developed within the cherty dolomites of the Ordovician-Silurian age Upper Whittaker Formation and shaly dolomites of the lower Road River Formation, along the axial plane of the Prairie Creek Anticline (PCA).

MQV type mineralization comprises massive to disseminated galena and sphalerite with lesser pyrite and tetrahedrite-tennantite in a quartz-carbonate-dolomite matrix. Secondary oxidation is variably developed, yielding mainly cerussite (lead oxide) and smithsonite (zinc oxide); tetrahedrite-tennantite has undergone only minor oxidation. Silver is present in solid solution with tetrahedrite-tennantite and to a lesser extent with galena. Veins dip steeply to the east; widths generally vary between less than 0.1 m up to 5 m, with an average horizontal thickness of approximately 2.7 m.

The MQV is the most extensively developed of the known mineral zones. Underground development and diamond drilling have demonstrated the continuity of the MQV over a horizontal strike length of 2.3 km. The MQV trends approximately north-south and dips between vertical and 40º east (average dip is 65º east). It remains open to the north and may continue for a further 4 km to the Rico showing. Diamond drilling has indicated continuity to a depth of at least 450 masl.

Mineralization is best developed in the more competent (brittle) units of the Lower Road River and Whittaker Formations; graphitic shale in the mid and upper parts of the Road River Formation is less competent and contained veins are poorly developed. For example, at the end of 930 mL the MQV can be seen to dissipate into the middle-Road River shales. As well, the vein does not appear to be well developed in the shales of the Cadillac Formation lying stratigraphically above the Road River Formation.

STK Mineralization
Towards the end of 930 mL at Crosscut 30, a series of narrow (average 0.3 m wide), massive sphalerite-galena-tennantite veins are developed at about 40º to the average trend of the MQV. These sub-vertical veins range in thickness from 0.1 to 0.5 m, have no apparent alteration halo, and are separated from each other by unmineralized dolomite. The veins are locally offset and cut off by fault planes and are difficult to correlate at the present level of information. This style of mineralization is referred to as STK, although it does not represent a true stockwork but rather a series of splays off the MQV. To date, STK-style mineralization has only been located in the immediate area surrounding the exposure in the 930 mL workings and through diamond drilling. There is also evidence that the STK may be exposed on surface towards the northern end of the main zone but is partially obscured by alluvium.

SMS Mineralization
SMS mineralization was discovered by NZC in 1992 while testing the depth extent of the MQV.

Mineralization is generally fine-grained, banded to semi-massive, and comprises massive fine-grained sphalerite, coarsegrained galena and disseminated to massive pyrite. Silver is contained in solid solution within both galena and sphalerite and the SMS mineralization contains no tennantite- tetrahedrite, very little copper, half as much galena, but substantially more iron sulphide/pyrite than typical vein mineralization. Fragments of SMS mineralization occur in vein mineralization indicating that the SMS predates the veins.

The majority of SMS mineralization occurs within the Mottled Dolomite unit of the Whittaker Formation, which the mineralization totally replaces without any significant alteration. SMS sulphides are developed close to both the vein system and the axis of the PCA and are presumably older than the vein mineralization. An apparent thickness of up to 28 m of SMS mineralization has been intersected in MQV drillholes, approximately 200 m below 883 mL.

MVT Mineralization
MVT mineralization found on the Property is comprised of colloform rims of sphalerite, brassy pyrite-marcasite and minor galena, with or without later dolomite infilling. The mineralization appears to occur discontinuously within coarse biohermal reefs of the Root River Formation, and always at approximately the same stratigraphic horizon. It appears to be classic MVT mineralization insofar as it occurs in open cavity-type settings.

Prairie Creek will be an underground mine extracting the majority of mineralized material from the steeply-dipping, narrow MQV. Smaller mineralized material quantities will be mined from the STK and SMS zones, generally later in the mine life. Three levels of adits (970 L, 930 L, 883 L) were established previously. Five shrinkage stopes were partly mined above the 930 and 883 levels, giving a stockpile of about 10,000 tonnes of mixed mill feed and waste that is currently located adjacent to the mill.

The MQV zone area covers a strike distance of about 2,100 m and a vertical distance of about 400 m. Below 883 L, mining levels will be established at generally 60 m intervals with 20 m sublevels. Initial stoping will start from the 883 L. As mining on the MQV progresses to depth, mineralized material mined will be supplemented by the STK and SMS zones. Lower levels will be developed to depth through ramp access over the first approximately five years of operation.

Mining will be by Longhole Open Stoping Longitudinal Retreat (LHOS) in the MQV vein and in the STK area. Longhole Upper Retreat Stoping (LUR) will be employed in the SMS area. An average mining rate of 2,400 tonnes per day of mineralized material is projected. At steady-state, approximately 864,000 tonnes of mineralized material per year will be mined. Mine life is projected to be 20.1 years from start-up of the processing plant.

MQV material will be the majority of mill feed production and will be extracted throughout the life of the mine. The vein structure is currently exposed in over 800 m of backs in the existing underground development.

The SMS mineralization occurs approximately 200 m below 883 L and will require significant underground development for access from mill feed development driven in the MQV.

LHOS will use electric-hydraulic drill jumbos and diesel-powered scoops for waste development. Mill feed development will use the same equipment in early years of production but with battery-powered scoops planned to be used in later years. Production drilling will be by conventional longhole drills. The SMS zone will use electric-hydraulic drill jumbos and dieselpowered scoops. Bolting will generally be accomplished by mechanized bolters; mineralized material and waste movement to surface will be via conventional truck haulage.

Longhole Open Stoping (LHOS)
Mining of the MQV will be by LHOS. The mining level in the mineralized material at the 883 m elevation has previously been established along a significant part of its length but will be slashed to 4.5 m W x 4.5 m H to serve as a mucking horizon. The average vein width is less than 4.5 m. Mining below the 883 level will require similar main levels, driven 4.5 m W x 4.5 m H, to be established every 60 m vertically; within this 60 m height there will be a sub-level driven every 20 m at 4.0 m x 4.0 m dimensions. Access to the sublevels will be gained by ramp and cross-cuts. Mill feed development in the vein will be for a distance of up to 250 m north and south (each side) of the access point. Slots will then be developed between sublevels followed by retreat LHOS towards the access in approximately 30 m panels. The lowest elevation sub-level will lead the mining front with all mineralized material being mucked from the main (mucking) level. Broken mineralized material will be drawn down in a controlled fashion so as to provide interim wall support and assist in minimizing wall dilution. Fill fences will be constructed on all levels other than the uppermost, after the extraction of each panel. The mining cycle will thus involve mill feed development, followed by drilling, blasting, mucking, and filling.

Mine design
The existing access via the 883L adit will be enlarged to 5.0 m H x 5.0 m W to provide appropriate main access from surface for personnel, equipment, fresh air and materials handling. The new ramp, following the plunge of the MQV, from the twinned portal will serve as the main access to the mine and internal ramp systems to access the ore. The ramps have been designed at a maximum +/-15% gradient with a minimum 30 m turning radius and remucks at 150 m intervals. Mineralized material remucks and truck loading areas will be sited at every level access to the MQV. Within the vein, the maximum distance between remucks is approximately 200 m.

Lateral and vertical development design
Sublevels will be accessed from the ramps on a 20 m vertical interval defined by the planned stoping heights. Ramp development will be set back typically 40 m (minimum 25 m) from the mill feed contact. This arrangement recognizes longterm geotechnical stability and provides adequate space for the placement of a return air raise and other services such as sumps, remucks, transformer bays and portable refuge locations.

Mineralized material drives in the MQV zone will typically be for a distance of up to 250 m each side of the access crosscut from the ramp. In the STK zone, mineralized material drives on a level will be driven in accordance with the geometry and mining sequence. The SMS zone will be accessed by a secondary ramp driven up from the south ramp at a gradient of 15%, with entry to the zone by a series of cross-cuts.

Development heading design considers equipment needs, mine services and regulatory requirements. Mineralized material drives at the base of a mining block will be used for mucking access and will be driven at 4.5 m x 4.5 m; sub-level mineralized material drives will be driven at 4.0 m x 4.0 m.

Paste fill will generally be the material used as backfill within the mine. A newly installed paste backfill plant will return 100% of the flotation tailings to underground.

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The current process design incorporates some existing equipment, which was moved from another mine and installed at Prairie Creek in 1981/1982. With the increase in throughput to 2400 tonnes per day (tpd), the crushing plant is the only area to be retained without modification. The DMS pre-concentration plant is new and will be fed using a new conveyor from the existing fine mill feed bin. A new ball mill will be added into the grinding circuit with the existing mill being refurbished. All of the flotation cells in the lead and zinc flotation circuits will be new to meet the required throughput with existing tanks refurbished for conditioning purposes. Reagent preparation system will be completed to modern standards for lead and zinc concentrate production.

Ahead of the process plant, the ROM area will include a stockpile used to even-out mine production against mill capacity. The processing plant consists of crushing, DMS pre-concentration, grinding, lead and zinc sequenti ........