Narrow vein deposits are common geological formations where significant concentrations of high-grade material can occur within narrow, often steeply dipping, veins or structures. Due to their shape and geometry these types of orebodies are challenging to mine using conventional methods. 

Why are steeply diping narrow vein deposits so challenging?

Vein Geometry 

Narrow vein deposits are characterized by the occurrence of ore within relatively narrow and often discontinuous veins or structures within the host rock. These veins can vary in width from centimetres to a few meters, with varying dips that can between roughly 60-90 degrees. As a result, mining companies would require costly in-fill drilling, typically on 25-meter centres or less to accurately define these deposits. 

Grade Variability 

The grade of narrow vein deposits can be highly variable along strike and down dip. Some sections of the vein may contain high-grade ore shoots where concentrations are economically viable, while others may have lower grades or even barren zones.  

Due to their challenges, these deposits often prove uneconomic to mine using conventional mining methods and are often left unmined. Open-pit mining generates significant waste and uneconomic strip ratios, while selective underground methods require costly infrastructure that quickly erode project returns.  

Novamera’s Surgical Mining Method 

Developed to mine a high-grade narrow vein deposit situated on the periphery of an open-pit gold operation, Novamera’s suite of technologies leverages hardware and software along with conventional drilling equipment to economically mine these deposits.  

Novamera’s Guidance Tool is deployed on a standard diamond–core rig down-dip of the orebody, scanning a 3-metre radius around the borehole at 1.5-metre intervals. Along with AI, software, and advanced algorithms, an accurate 3D model of the orebody can be created that accurately shows the vein’s geometry, volume, and continuity. This process captures 4900% more data than infill drilling at a fraction of the cost. This technology allows the miner to reduce risk during the production process by adapting the drill plan and dip angle to match the real orebody geometry.  

The Smart Drilling System, which includes a Positioning Control System and Course Correction device, is paired with a large-diameter drill to maintain the prescribed trajectory defined by the Guidance Tool. Reverse circulation with air-lift assists in efficiently bringing ore to the surface, where it can be transported to a mill for processing.  

This two-pass sequence continues down the vein’s strike length; a series of primary holes are drilled, and every other hole is backfilled with paste-fill. This allows the option of overlapping production holes and also stabilizes the ground while providing real-time reclamation.  

Advantages 

• It requires significantly less capital and development than underground long-hole stoping, providing significantly higher NPV and IRR values.  

• Guidance Technology radically reduces dilution, continuously optimizing recovery throughout the mining process.  

• Equipment is easily mobile, allowing mining companies to access remote areas, move quickly to high-value areas, optimize cash flow, and adapt to changing commodity prices.   

• Due to its small footprint and low environmental impact, it can drastically reduce permitting timelines and take advantage of small mining permits.  

• The closed-loop system recycles water, creating minimal water discharge into the surrounding environment.  

• The process does not involve blasting and operators stay above ground and away from the mine face, providing a safer environment for miners.  

Conventional Narrow Vein Mining Methods (cost comparision below) 

Cut and Fill 

This method involves mining ore in horizontal slices (cuts), starting from the bottom of the vein and working upwards. Once a cut is excavated, the mined-out area (fill) is backfilled with waste rock, cemented tailings, or other materials to support the next cut above it. Cut and fill is particularly suitable for irregularly shaped veins and allows for high ore recovery rates. 

Advantages:  

• Effective for irregular ore bodies that are difficult to mine with other methods. 

• Enables the recovery of high-value metal deposits in weak rock. 

• Allows for selective mining in deposits with specific spatial characteristics. 

• Faster stope production. 

• No inventory tied up in stope. 

Disadvantages:  

• Generally, more expensive and requires suitable backfill, tailings or coarse aggregate. 

• It can be slow because of the additional process of backfilling and ground support. 

Cut and Fill (Mechanized)

In mechanized cut and fill mining, specialized equipment such as loaders, haul trucks, and drilling rigs are used to mechanize the process of cutting ore and filling the stopes with waste material or backfill. This method improves efficiency and safety in narrow vein mining operations. 

Advantages 

• Accommodates wider veins (requires slightly wider veins) to utilizes jumbos and load-haul-dumps for efficiency. Automation reduces manual labour.

Disadvantages 

• Less flexible than conventional method and has a higher initial equipment cost.  

Room and Pillar Mining

Although typically used in coal mining, room and pillar mining can be adapted for narrow vein mining where the ore body is relatively thick compared to its width. It involves leaving behind pillars of ore to support the roof while the surrounding ore is extracted. This method requires careful design to balance ore recovery with stability. 

Advantages:  

• Can have higher productivity and lower cost  

Disadvantages: 

•  If valuable pillars cannot be removed there could be high ore loss. 

Shrinkage Stoping

In shrinkage stoping, ore is removed in horizontal slices similar to cut and fill, but instead of backfilling immediately, the unsupported ore in the stope naturally caves into the extraction level below as the ore is removed. This method requires careful sequencing of mining activities and provides good ore recovery rates, but it can be labour-intensive and requires good ground conditions. 

Advantages:  

• Limits dilution, often more cost effective for narrow zones and often the only alternative before Surgical Mining was developed.  

• Maintains stability for the hanging wall while the ore remains in place.  

Disadvantages:  

• Limited to steeply dipping ore bodies.  

• Considerable value (60%) of value remains in stope until entire panel is completed. 

• Not flexible for sudden changes in dip.   

• Very labour intensive and requires strict coordination and planning when excavating the swell.  

• Increase liabilities, as this method can be very dangerous.  

Longitudinal Retreat Mining

Long-hole mining involves drilling parallel holes along the length of the ore body from a main access drift. Explosives are then used to blast the ore, which is subsequently mucked out and transported to the surface. Longitudinal retreat mining is efficient for continuous extraction along the length of narrow veins and can be mechanized to some extent. 

Advantages:  

• Can produce high tonnage with less development.  

Disadvantages:  

• Hole deviation can result in dilution or poor fragmentation.  

Sublevel Longhole

Sublevel stoping is a variation of open stoping that involves dividing the ore body into horizontal slices or sublevels. Each sublevel is mined progressively, starting from the bottom, with drilled holes for blasting and ore removal. The method allows for selective ore mining and can be adapted to varying vein widths. 

Advantages:  

• Low cost and efficient non-entry production operations,  

• Utilisation of highly mechanised, mobile drilling and loading production equipment 

• High production rates with a minimum level of personnel, furthermore, production operations are concentrated into few locations such as ring drilling, blasting and drawpoint mucking. 

Disadvantages:   

• Rapid changes in vein width may not be seen, and long–holes may wander “off vein” if ground conditions change.  

• Requires significant level of development infrastructure before production starts, thus incurring a high initial capital investment. 

Cost Comparision Narrow Vein Mining Methods