| Abstract: | An orientation survey was conducted over the Quartz Mountain, Oregon, hot-spring type disseminated gold deposit to address three questions critical to successful exploration of the area: What is the relationship between bedrock geology and the trace-element content of trees and soils; do these relationships change seasonally; are these relationships similar in the two tree species which discontinuously blanket the area?Twig, needle and wood samples were collected four times during the year from both ponderosa pine (Pinus ponderosa) and white fir (Abies concolor). Soils were collected once. All samples were analyzed for Au and As and the wood samples were analyzed also for Sb.Arsenic was the best pathfinder element, having little analytical, spatial, or seasonal variation in the twig and needle samples. Anomalous levels were 150 μg/g (ppm) As in pine and 30 μg/g in fir. Gold showed analytical variation of 20–30%, sample duplicate variation up to 90%, spatial changes, and seasonal variation ranging from winter-summer background 10–20 ng/g (ppb) Au] to anomalies of 300–400 ng/g (ppb) Au in pine and 100 μg/g (ppb) Au in fir in the spring and fall. Antimony could not be completely evaluated as a pathfinder element because it was only determined in wood samples.Needles and twigs from both species proved to be viable sample media for exploration of the area. Wood was not a suitable medium because of low, erratic values, perhaps due in part to analytical technique. Needles had 2 to 20 times higher As concentrations than did twigs. Twigs had a slightly higher Au content 25 ng/g (ppb)] than did needles. The pine samples were higher in both elements than were the fir samples. The data, normalized by species, could be treated as one homogeneous data base.The soil Au and As data outlined the mineralization clearly with a central Au anomaly 100 ng/g (ppb) and greater] surrounded by As anomalies 100 μg/g (ppm) and greater] over a distance of 594 m. Neither spring nor fall tree Au anomalies were coincident with the soil Au anomaly. Consistent throughout the year, tree As anomalies coincided with the soil As anomalies, but covered a smaller area. Both the Au and As anomalies in trees appeared to be related to bedrock contact zones rather than to the soil the trees were growing in. |
