Geology Reference
In-Depth Information
et al., 2001, p. 143). Peat, which is a commonly used fuel with recognizable plant material and high water content,
contains only 5400 BTU/lb.
The burning temperature for specific plants, such as
, is not available; however, wood burns at
approximately 600°C (Vogel, 2003), and, because of its carbon content, coal burns at higher temperatures, from
1300°C to 1600°C, depending on rank (IEA Clean Coal Centre, 2006). Therefore, the 1320°C temperature of the
Tschudi burn (Lechtman and Moseley, 1975, pp. 161
Tillandsia
162) is more consistent with the higher temperatures and
higher BTUs of a coal-fueled fire and not the lower temperatures and BTUs of a plant-fueled fire.
-
Calcium in the Soil
P
revious geochemical studies of the deeply burned adobe walls at the Tschudi burn showed no anomalous metal
content and hand samples contained no copper prills that would be evidence of copper processing. However, the
soil within the burn had not been similarly studied. If metallurgy had taken place at the site at any time in the past,
then analyses of soil samples would have elevated metal content with respect to the background. Therefore, eight
reconnaissance soil samples were taken at ~10 m intervals at 10
four sieved
samples were taken outside the burned area to establish background metal concentrations and four sieved samples
were taken within the burned area. Samples were collected with a plastic trowel and plastic sieves were used to
avoid any metal contamination. These soil samples were submitted to a commercial exploration assay laboratory
for multielement, induced coupled plasma (ICP) analysis. The analyses showed uniformly low gold (
-
20 cm depth across the Tschudi burn
—
5 ppm) and
<
silver (
0.05 ppm) content of the soil samples from inside and outside the burned area (Table 4.1.1). There was no
difference between the copper content of the soil outside the burned area (11
<
-
15 ppm) and the copper content of the
soil within the burned area (11
16 ppm). The analyses from this soil survey confirmed, as previous studies had
shown (Lechtman and Moseley 1975, Table III; Brooks et al., 2004) that there was no geochemical evidence for
metallurgy at the site.
-
However, the soil data showed that the calcium content of the soil inside the burned area (8300
-
18 000 ppm) was
higher than the calcium content of the soil outside the burned area (7200
10 000 ppm) (Table 4.1.1). This indicated
that calcium was present, either during or after the burn, in the soil samples. Possible sources included human bone
from reported cremation (La Rosa in Squier, 1877, p. 141); shell fragments used in the adobe, which contained
1
-
6 wt% CaO (Lechtman and Moseley, 1975, Table III); mouse bones or osseous inclusions (Lechtman and
Moseley, 1975, p. 149); or, perhaps, the fuel used for the burn.
-
Table 4.1.1
Analyses from soil geochemical traverse across the Tschudi burn, Chan Chan, northern Peru.
ICP analyses from American Assay Laboratories, Sparks, Nevada.
Trace elements in soil, inside and outside of burned area
Ag (ppm)
*
Element concentration
Au (ppm) Cu (ppm) Ca (ppm) P (ppm) K (ppm) B (ppm) S (ppm)
Sample number
SS 1
0.05
5
15.3
7257
1254
3514
11
166
<
<
SS 2
0.05
5
13.6
7557
1157
3653
14
184
<
<
SS 3
0.05
5
14.1
8357
1395
4395
21
1202
<
<
SS 4A
0.05
5
16.2
18186
1916
6120
32
9733
<
<
SS 4B
0.05
5
10.8
10947
2260
5867
30
2635
<
<
SS 5
0.05
5
13.1
17960
1696
5763
38
6981
<
<
SS 6
0.05
5
11.0
10274
1141
3092
15
193
<
<
SS 7
0.05
5
11.4
9752
1401
3244
11
463
<
<
Note
: Samples 1, 2, 6, and 7 were taken outside the burned area to establish background. Samples 3, 4A, 4B, and 5 were taken inside the burned
area.ppm, parts per million.
