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HardRock Aggregates
HARD Rock Aggregates

The proposed Mulberry Mine is located at 2173 Mulberry Road, Cabarrus County, Concord, North Carolina. The Mulberry Mine plans to product crushed stone products from the mining and crushing of granite and diorite bedrock. These materials are considered a potential source of coarse aggregates at this site. Construction aggregates are hard, essentially inert materials suitable for being formed into stable mass in their natural form to produce a road or foundation fill.

The site is located in the Inner Piedmont Physiographic Province. The underlying bedrock generally consists of syenite granite of Concord plutonic suite (Devonian and Silurian). The surficial geologic materials in this area consist mainly of weathered rock material underlain by shallow igneous and metavolcanic rocks. The metavolcanic rocks are either felsic, mafic, and/or both.. The syenite rock is typically coarse grained, light bluish grey and is composed of potassium feldspar, augite, plagioclase, hornblende, and biotite. The syenite body is an elliptical outcrop pattern approximately 5.5 miles in diameter. The syenite was first quarried for railroad ballast in the early 1900’s and also used as a polished stone.

An exploration program was developed based the local geologic map, the site topography and spacing of the drill holes less than 1,320 feet apart. The initial drilling plan was prepared to define the overburden thickness and evaluate potential fine grain aggregate use, and collect limited rock core samples for preliminary testing.

Chemical properties of crushed stone are important in determining its suitability for use in cement, concrete, and road base. The aggregate most ideally should be inert and not change chemically during use. Some rocks contain minerals that are chemically reactive in Portland cement, bituminous concrete or asphalt. In cement, alkali-silica reactivity can occur when silica reacts with alkali in the cement to form a gel around aggregate particles. The gel expands, causing spalling of the concrete. This generally occurs only where the rock contains silica in the form of natural glass, chalcedony, opal, chert, finely divided quartz, and strained quartz.

Sulfides such as pyrite, if present in the rock, can react with oxygen and water to form iron hydroxides and sulphates. This will produce discoloration and weakening of the cement.

Rocks with high silica contents have negative surface electrical charges and, as a result, attract moisture. Moisture along the surface of the rock grain breaks down the adhesion between the grain and bituminous material in asphalt, creating a condition called stripping. For this reason, some quartzite’s, gneisses, granites, and schist’s with very high quartz contents may induce stripping in asphalt. Surfactant chemicals are added to reduce this effect.

Physical properties critical for performance of crushed stone include strength or durability, porosity and pore size, and volume integrity (maintenance of constant volume) while being subjected to freezing and thawing conditions. The natural habit of breaking into cubic or relatively cubic particles on crushing is also important.

Aggregate quality of igneous rocks like granite and diorite is determined by the strength of interlocking bonds between quartz, amphiboles, and biotite. Fine to medium grained, mafic igneous rocks such as diabase, gabbro, and diorite are highly resistant to abrasion due to the strength of interlocking grains. More felsic igneous rocks are less resistant to abrasion, but generally have a strength that is quite suitable for use as aggregates.

Full quarry development of the property projects an 88-acre pit containing 36,816,000 tons of aggregate..

The Mulberry Mine processing plant production will be designed at production rate of 500-tons/hr (tph) or 300,000 Tons Per Year (TPY) from initial start up to 1,1,00,00 TYP at full capacity projected for year 5. The material handling process was simulated by AggFlow software for material balance estimation. This plant may be operated to produce rail road ballast, roadway materials, and cement aggregates.

We propose to use the following rock crushing and processing plant:

  • Apron Feeder/500 Ton Storage Bin
  • Lippmann 36 x 50- Primary Crusher
  • 2-FLSmidth Raptor XL400 S/M- -Secondary and Tertiary Crusher (Standard Head and Short Head)
  • 9- Conveyors and Screens (1-Single, 1-Double, and 2-Triples)


The surface mine operation will be a truck and shovel pit mine operation for aggregate production. The following quarrying equipment is anticipated for this surface operation:

  • Drill -Atlas Copco Roc (F9C)
  • Excavator-Caterpillar 336F
  • Haulage Trucks-Caterpillar 770 (2)-40 ton
  • Wheel Loader-Caterpillar 966M
  • Water Truck/Fuel Truck

A cash flow analysis was developed based on mining the initial 6.8 million tons for 8 years. The cash flow analysis was based on using the average sale price of $16/ton for ABC stone, #57stone, #78, and rail road ballast local to the Charlotte, NC area. The analysis will require further refinement to obtain actual bids for mine development and equipment. We have estimated the Acquisition and Capital Cost at $10.7 M, plus the development cost of $0.98 M., and plus $0.5 M working capital or a total of $12,180,000 investment.

The After Tax Discount Cash Flow Rate of Return (DCFROR) is projected at 31%. The cash flow analysis projects the quarry to generate a Net Present Value of $12 M profit above Capital Investment financed at 12%, after the first 8 years of operation.

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