Pulacayo Project Feasibility Study - Apogee Silver

Pulacayo 1 000 t/d Phase I Feasibility Study - NI 43-101 Technical Report
090644-3-0000-20-IFI-100
These results are further improved by proceeding with a cyclone desliming step ahead
rougher flotation (see Figure 13.2) to reduce the amount of slimes in the feed (Test N° 2).
However, around 9.9% Ag is lost in the slimes fraction or discarded overflow (20% in weight).
Native silver occurs as fine particles of size smaller than 20 µm (see section 13.3.2).
The Low Grade (LB) sample with a grind size of d80 150 µm, the LCT results shows that the
differential flotation is able to recover almost 30% of silver in the lead concentrate (with a
mass pull of 0.53%) and 20.9% of silver in the zinc concentrate (with a mass pull of 1.28%).
The lead and zinc concentrate grades are 46.7% and 44.8%, respectively. Also, the lead and
zinc recoveries are estimated as 34.6% and 50.9%, respectively. The silver grades in the
lead and zinc concentrates were reported as 2,600 g/t and 749 g/t, respectively (Test N° 1).
Lead recovery was low with a substantial amount of the zinc tied up in the lead circuit cleaner
concentrate.
These results are further improved by proceeding with cyclone desliming step ahead rougher
flotation to reduce the amount of slimes in the feed (Test N°2 and Test N° 3). However, 5% to
11% Ag is lost in the slimes fraction or discarded overflow (27% and 26% in weight). Native
silver occurs as fine particles of size smaller than 20 µm (see section 13.3.2). The lime
consumption is reported to be as high as 14.3 kg/t.
It is not clear from the test work data and reports the extent to which this closed circuit test
approached the locked cycle test standards commonly used in the industry. There is no
information on how many cycles were performed (usually six) and whether circuit stability
was reached as the circulating loads of middlings approached a sort of equilibrium. The most
likely consequence of not attaining equilibrium is that concentrate grades may be overestimated
and recoveries under-estimated.
However, the results seem to be reasonable and in accordance with expectations from the
mineralogy of the ore. Further testing was undertaken by ED&ED and their findings are
shown later. These results constitute the design basis for the flow sheet.
Full open-circuit tests (OCT) of sulphide minerals flotation were conducted initially on each
sample as a proof of concept of the overall circuit and to establish a workable set of flotation
conditions and reagents. These test demonstrated that sulphide flotation to saleable lead and
zinc concentrates at acceptable (for batch tests) recoveries was possible.
OCT flotation flow sheet was developed incorporating a moderate grind size of 150 µm
(P80). The pH in the lead rougher circuit was elevated to a value in the range of 9 to 10 using
lime. The pH in the zinc rougher circuit was maintained in the range of 10 to 11. AF-242 and
Z-11 were used as the lead and zinc collectors, respectively. A regrind step to produce high
grade concentrate was not considered. In the lead flotation circuit, Sodium Cyanide (NaCN)
and Zinc Sulphate (ZnSO 4 .7H 2 0) were used as pyrite and sphalerite depressors, respectively.
The pH of the cleaning stages in the lead concentrate was maintained at the range of 9 to 10
using lime. The pH in the zinc circuit cleaning stages was elevated to activate spharelite and
lime was used to raise the pH to above pH 10 to depress iron (pyrite).
According to the mineralogy studies carried out by ED&ED (see section 13.3.2), galenasphalerite
assemblage (intertwined specimens) is present at some extend. This may be
reason for some not desired zinc content in the lead concentrates. In addition, unwanted
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