Difference between revisions of "Cutoff grade estimation"
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CutOff grade is the minimum amount of valuable mineral in a given mining unit required to mine (or process) at a profit. Material above this grade is considered to be ore, and material below this grade is considered to be waste. 
CutOff grade is the minimum amount of valuable mineral in a given mining unit required to mine (or process) at a profit. Material above this grade is considered to be ore, and material below this grade is considered to be waste. 

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Usually expressed as: 
Usually expressed as: 

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−  == [[1.0 Calculating the CutOff Grade 1]] 

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−  '''1.1 BreakEven and Internal 1 

−  1.2 Lane’s Method 2''' 

−  1.3 Equivalent Grade 3 

−  2.0 Mineral Classification 4 

−  2.1 GradeTonnage Curves 4 

−  3.0 Adjusting the CutOff Grade 5 == 

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The most simplistic way to determine cutoff grade utilizes the following formula: Equation 1. 
The most simplistic way to determine cutoff grade utilizes the following formula: Equation 1. 

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−  +  === Lane’s Method === 

Lane’s Method offers a more accurate and complex way to calculate cutoff grade. This method also requires more information, so it may not be the first choice for a preliminary calculation. Although there are many intermediate grades determined through Lane’s Method, there is ultimately only one output cutoff grade. 
Lane’s Method offers a more accurate and complex way to calculate cutoff grade. This method also requires more information, so it may not be the first choice for a preliminary calculation. Although there are many intermediate grades determined through Lane’s Method, there is ultimately only one output cutoff grade. 

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Qr Refining capacity 
Qr Refining capacity 

−  +  === Equivalent Grade === 

The following formula can be used to classify the equivalent grade for a mining unit: 
The following formula can be used to classify the equivalent grade for a mining unit: 

G = g1 + f2g2 + f3g3 + … 
G = g1 + f2g2 + f3g3 + … 

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This is necessary for polymetallic deposits in which the value of a block may be influenced by more than one valuable mineral. It simplifies the value of the block so that cutoff grade analysis can be performed, and a decision of whether or not to mine the block can be made. 
This is necessary for polymetallic deposits in which the value of a block may be influenced by more than one valuable mineral. It simplifies the value of the block so that cutoff grade analysis can be performed, and a decision of whether or not to mine the block can be made. 

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+  == Mineral Classification == 
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Increasing the cutoff grade places a stricter requirement on what can be considered ore. This decreases the amount of material that can be considered ore, and with it the reserves and life of mine. 
Increasing the cutoff grade places a stricter requirement on what can be considered ore. This decreases the amount of material that can be considered ore, and with it the reserves and life of mine. 

−  +  === GradeTonnage Curves === 

GradeTonnage curves are a visual representation of the impact of cutoff grades on mineral reserves. 
GradeTonnage curves are a visual representation of the impact of cutoff grades on mineral reserves. 

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+  == Adjusting the CutOff Grade == 
Revision as of 00:07, 4 February 2015
CutOff grade is the minimum amount of valuable mineral in a given mining unit required to mine (or process) at a profit. Material above this grade is considered to be ore, and material below this grade is considered to be waste. Usually expressed as:
 g/t
 $/t
 %
Contents
Calculating the CutOff Grade
BreakEven and Internal
The most simplistic way to determine cutoff grade utilizes the following formula: Equation 1. G=(c+m_om_w)/(y(sr)) Table 1: Basic CutOff Grade Parameters mo cost to mine ore mw cost to mine waste r refinery unit cost c cost to process ore y metal recovery s unit metal sale price
For the Internal (Milling) cutoff grade, mw = mo. This is simplified in Equation 2. Material below this grade should not be processed whether or not it has already been mined. G_Mill=c/(y(sr)) For the Breakeven (Mining) cutoff grade, mw = 0. This is simplified in Equation 3. Material below this grade should not be mined. G_Mine=(c+m_o)/(y(sr))
These cutoff grades are the fastest way to classify ore and waste, however, in a more detailed analysis they should not be relied on.
Lane’s Method
Lane’s Method offers a more accurate and complex way to calculate cutoff grade. This method also requires more information, so it may not be the first choice for a preliminary calculation. Although there are many intermediate grades determined through Lane’s Method, there is ultimately only one output cutoff grade.
Table 2: Lane’s Method CutOff Grade Parameters y Recovery C Concentrator capacity R Refining capacity f Fixed costs s Sale price c Concentrator costs r Refining costs V Present value d Discount rate
g_c=(c+(f+dV)/C)/(y(sr))
g_r=c/(y(sr(f+dV)/R))
gmc = f(Qm,Qc,gradedistribution) grc = f(Qr,Qc,gradedistribution) gmr = f(Qm,Qr,gradedistribution) Qm Mine capacity Qc Concentrator capacity Qr Refining capacity
Equivalent Grade
The following formula can be used to classify the equivalent grade for a mining unit: G = g1 + f2g2 + f3g3 + …
Failed to parse (syntax error): {\displaystyle G = g1 + f2g2 + f3g3 + …} This is necessary for polymetallic deposits in which the value of a block may be influenced by more than one valuable mineral. It simplifies the value of the block so that cutoff grade analysis can be performed, and a decision of whether or not to mine the block can be made.
Mineral Classification
Cutoff grades are used to determine the point at which material becomes economically valuable. Therefore, they are necessary to define the amount of ore in a deposit. The classification of ore depends entirely on cutoff grade. Increasing the cutoff grade places a stricter requirement on what can be considered ore. This decreases the amount of material that can be considered ore, and with it the reserves and life of mine.
GradeTonnage Curves
GradeTonnage curves are a visual representation of the impact of cutoff grades on mineral reserves.
Figure 1: An Example GradeTonnage curve (J.M. Rendu) Metal value is not the only factor affecting the profitability of a block. The presence of unwanted (often hazardous) material in a block may increase the processing cost [SME reference]
Adjusting the CutOff Grade
Stockpiling and blending are often used to ensure consistency of mill feed. This can affect cutoff grade since If the metal price increases, it may seem intuitive to lower the cutoff grade since the low grade material can be mined at a profit. However, the better decision is often to increase the cutoff grade instead. Processing the higher grade material will yield an increase in the amount of valuable mineral produced. This is assuming that the processing capacity does not change; only the ore being processed does. The extra product can then be sold at this increased price.
Extraction Sequence and Variable Grade Interprocess Options
 Polymetallic Deposits & Metal Equivalencies
Selectivity and Dilution Constraints Stock Piling and Pushback Factors Opportunity Costs, Discount Rates, and NPV Equation 1: Interprocess Options
In the case of multiple processing options U1G1 = U2G2 utility This means that if process A is cheaper than process B, the cutoff grade for process A