events, where a deposit first reaches the 50% coverage threshold. The cumulative recovery AUC likewise increased from 14.04 to 83.15. Case 2. Alemão: Multivariate TMI + Radiometric Alemão was selected as the representative multivariate case because it provides a direct comparison between single-variable rankings and a fused workflow. In this case, sPCA was first applied separately to each variable, the retained score vectors were concatenated and standardized, and similarity was then computed in the fused space using deposit-based weights. The resulting top-ranked windows from the combined TMI + radiometric U analysis are shown in Figure 11. Using Alemão as the training deposit (Deposit 3) and Deposits 1, 2, 4, and 5 as test deposits, sPCA Multi achieved the strongest validation performance, recovering 77.7% of the total test-deposit area by rank 250 (Figure 12). This exceeded sPCA Univariate Radiometric U, which recovered 52.8%, sPCA Univariate TMI, which recovered 31.0%, and Raw Multi, which recovered only 7.9%. The fused multivariate ranking was also the only approach to produce hits for all four test deposits, with the first threshold-reaching hit occurring at rank 11. Discussion This study aimed to develop a quantitative, reproducible, and interpretable framework for geophysical prospecting based on spatial similarity to a known deposit. The results of both case studies support that objective. Rather than comparing windows only in the original pixel space, the sPCA approach decomposes the reference anomaly into spatial modes and ranks candidate windows according to how strongly they reproduce those deposit-specific patterns. An important Figure 11 - Cumulative recovered fraction versus prediction rank for the Paulo Afonso (Dep. 6) univariate TMI case, comparing Raw Univariate TMI and sPCA Univariate TMI (K = 17). Yellow markers denote overlap events and red markers denote hit events, with labels indicating the corresponding deposits. Figure 12 - Recovered fraction as a function of prediction rank for selected deposits in Case 2, comparing univariate and multivariate ranking strategies. sPCA Multi achieves the highest overall recovery, while overlap and hit markers indicate how rapidly the test deposits are recovered.
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