URUANA — SÃO DOMINGOS STRUCTURAL-NODE AUDIT

Mapped structural node:
- The concealed and exposed São Domingos segments share exactly the same endpoint.
- This mapped exposure/concealment transition lies ~8.113 km from Uruana.
- The two mapped segments are essentially collinear at the join (deflection ~3.1° from a straight continuation), so this is not a bifurcation; it is an exposure/cover transition.

Independent traverses near this node:
- Production line 10 (E–W), 02/09/2008: crosses São Domingos only ~86 m from the mapped transition.
  Raw-field step = 13.426 nT; An_Mag step = 11.743 nT.
- Tie-line 9120 (N–S), 01/07/2008: crosses the same concealed segment ~1.35 km from the transition.
  Raw-field step = 7.110 nT; An_Mag step = 3.315 nT.
- The flights are orthogonal and separated by ~63 days.
- In both traverses, movement toward the same NE side of the mapped fault corresponds to an increase in magnetic field.
- Magnitudes differ, so this is directional/qualitative replication, not equality of gradient amplitude.

Along-fault behavior:
- The absolute An_Mag step is largest within the first ~15 km from the transition and collapses farther north.
- Exploratory association of |An_Mag step| with distance from the transition:
  Spearman rho ≈ -0.879 (post-discovery descriptive; not confirmatory).
- Surface lithology does not trivially explain the strongest two traverses:
  line 10 is mapped as alluvium on both sides; line 20 as Serra de Santa Helena on both sides.
  Thus the strong step does not require a mapped surface lithologic contact.

Interpretation:
The cleanest current model is a localized magnetic intensification along the São Domingos fault zone near Uruana, independently observed by orthogonal flights on different dates. The exposed↔concealed cartographic transition is spatially coincident with the strongest sector, but should not itself be interpreted as a tectonic bifurcation.