Abstract A multiparameter, helicopter-borne magnetic, electromagnetic, and radiometric survey completed in 1995 covered the entire Bathurst Mining Camp, northeastern New Brunswick. The resulting unique and coherent high-resolution data set was used to improve detailed geologic mapping of the region. It also allowed the characterization of the geophysical response of massive sulfide deposits in the Camp. The five-frequency, multicoil helicopter-borne magnetic, electromagnetic system used for this survey covers a wide frequency range and allows for detailed conductivity mapping of the ground. In particular, the apparent conductivity map generated from the 4,433-Hz coplanar electromagnetic data outlines clearly many textures of the bedrock geology. Conductive units are distinct, very well defined, and can be used to help supplement detailed geologic mapping. Moreover, the conductivity maps show excellent correlation with the calculated first vertical derivative of the magnetic field, providing a means to distinguish between overburden and bedrock conductivity responses. Many orebodies are associated with discrete, coincident magnetic and conductivity anomalies. The survey was instrumental in the discovery of the small Camelback massive sulfide deposit. Although the deposit is not economic, this shows that modern sophisticated surveys can lead to new discoveries in a mature mining camp.

Abstract Sulfide deposits in the Bathurst Mining Camp, where hosted by felsic volcanic and/or fine-grained sedimentary rocks in both the footwall and hanging wall, are associated with discrete gravity highs. Even when the local gravity field is influenced by signals produced by neighboring mafic-intermediate volcanic rocks or mafic intrusions, the signal related to a deposit can invariably be distinguished, either as itself or as a filtered enhancement. The presence of distinct signatures is primarily a function of the proximity of these deposits to the bedrock surface. Generally they are located no more than a few meters beneath the ubiquitous glacial overburden. The potential of the gravity method for finding more deeply buried sulfide deposits in the Bathurst Mining Camp is demonstrated by discovery of the Maybrun mineralized zone under roughly 180 m of younger sedimentary cover. Gravity anomalies related to near-surface deposits range in amplitude from the exceptionally large 4-mGal amplitude, premining signature of the 12 million metric ton (Mt) Brunswick 6 deposit to very small anomalies, such as the 0.25-mGal amplitude anomaly associated with the 1.1 Mt Key Anacon deposit. There is no linear relationship between tonnage and amplitude for the deposits of the Bathurst Mining Camp, although a linear relationship, albeit with a moderate degree of scatter, is apparent between amplitude and deposit thickness. The largest deposit in the Bathurst Mining Camp, the giant 122 Mt Brunswick 12 orebody, produces a signal of just 1.0-mGal amplitude, an apparent inconsistency induced by large volumes of dense mafic volcanic rocks in the hanging wall. These produce a positive gravity signature that partially obscures the signal produced by the deposit, which otherwise would have an amplitude of about 3.5 mGal. In addition to being a source of interference, mafic volcanic rocks and mafic intrusions are the main cause of ambiguity in selecting singular gravity anomalies for further exploration.

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