Evaluation of Underground Zinc Mine Investment Based on Fuzzy-Interval Grey System Theory and Geometric Brownian Motion

Table 1

Input parameters.

Mine ore production (t/year)						100 000
Zinc grade (%)						[4.2, 5.0] = [0.042, 0.050]
Metal content of concentrate (%); 𝑚con−𝑚mr=(𝑚con%−8)⋅100𝑚con%≤85%;𝑚con%−8(𝑚con%−8⋅100)𝑚con%>85%;85%						[47, 52] = [0.47, 0.52]; [39, 42] = [0.39, 0.42]
Mill recovery (%)						[75, 80] = [0.75, 0.80]
Metal price ($/t)
	2009	2010	2011	2012	2013
January	1203	2415	2376	1989	2031
February	1118	2159	2473	2058	2129
March	1223	2277	2341	2036	1929
April	1388	2368	2371	2003	1856
May	1492	1970	2160	1928	1831
June	1555	1747	2234	1856	1839
July	1583	1847	2398	1848	1838
August	1818	2047	2199	1816	1896
September	1879	2151	2075	2010	1847
October	2071	2374	1871	1904	1885
November	2197	2283	1935	1912	1866
December	2374	2287	1911	2040	1975
Initial (capital) investment ($)						[3000000, 4000000]
Operating costs, geometric Brownian motion,; yearly time resolution ($/t), equation (39); Number of simulations						Spot value 32; drift 0.020; cost volatility rate 0.10; 𝑆=500
Construction period (year)						3 2014;2015;2016
Mine life (year)						5 2017;2018;…;2021
Discount rate (%)						[7, 10] = [0.07, 0.10]