The discriminant $\Delta$ of a quadratic equation $ax^2 + bx + c = 0$ is given by the formula:
\[
\Delta = b^2 - 4ac
\]
For the equation $3x^2 - 2x + \frac{1}{3} = 0$, we identify the coefficients:
\[
a = 3, \quad b = -2, \quad c = \frac{1}{3}
\]
Now, calculate the discriminant:
\[
\Delta = (-2)^2 - 4 \times 3 \times \frac{1}{3}
\]
\[
\Delta = 4 - 4 = 0
\]
Step 2: Conclusion.
Therefore, the discriminant of the equation is $0$, so the correct answer is (D).