The heavy-fermion compound

{CeCu}_{6 - x} {Au}_{x}

has become a model system for unconventional magnetic quantum criticality. For small Au concentrations

0 \leq x < 0.16

, the compound undergoes a structural transition from orthorhombic to monoclinic crystal symmetry at a temperature

T_{s}

with

T_{s} \to 0

for

x \approx 0.15

. Antiferromagnetic order sets in close to

x \approx 0.1

. To shed light on the interplay between quantum-critical magnetic and structural fluctuations we performed neutron-scattering and thermodynamic measurements on samples with

0 \leq x \leq 0.3

. The resulting phase diagram shows that the antiferromagnetic and monoclinic phase coexist in a tiny Au concentration range between

x \approx 0.1

and 0.15. The application of hydrostatic and chemical pressure allows us to clearly separate the transitions from each other and to explore a possible effect of the structural transition on the magnetic quantum-critical behavior. Our measurements demonstrate that at low temperatures the unconventional quantum criticality exclusively arises from magnetic fluctuations and is not affected by the monoclinic distortion.

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